Fast-path apparatus for receiving data corresponding to a TCP connection

ABSTRACT

A system for protocol processing in a computer network has an intelligent network interface card (INIC) or communication processing device (CPD) associated with a host computer. The INIC provides a fast-path that avoids protocol processing for most large multi-packet messages, greatly accelerating data communication. The INIC also assists the host for those message packets that are chosen for processing by host software layers. A communication control block for a message is defined that allows DMA controllers of the INIC to move data, free of headers, directly to or from a destination or source in the host. The context is stored in the INIC as a communication control block (CCB) that can be passed back to the host for message processing by the host. The INIC contains specialized hardware circuits that are much faster at their specific tasks than a general purpose CPU. A preferred embodiment includes a trio of pipelined processors with separate processors devoted to transmit, receive and management processing, with full duplex communication for four fast Ethernet nodes.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit under 35 U.S.C. §120 of U.S.patent application Ser. No. 10/092,967, entitled “FAST-PATH APPARATUSFOR RECEIVING DATA CORRESPONDING TO A TCP CONNECTION,” filed Mar. 6,2002, by Laurence B. Boucher et al., which in turn claims the benefitunder 35 U.S.C. §120 of U.S. patent application Ser. No. 10/023,240(Attorney Docket No. ALA-006A), entitled “TRANSMIT FAST-PATH PROCESSINGON TCP/IP OFFLOAD NETWORK INTERFACE DEVICE,” filed Dec. 15, 2001, byLaurence B. Boucher et al., which in turn claims the benefit under 35U.S.C. §120 of U.S. patent application Ser. No. 09/464,283 (AttorneyDocket No. ALA-006), entitled “INTELLIGENT NETWORK INTERFACE DEVICE ANDSYSTEM FOR ACCELERATED COMMUNICATION”, filed Dec. 15, 1999, by LaurenceB. Boucher et al., which in turn claims the benefit under 35 U.S.C. §120of U.S. patent application Ser. No. 09/439,603 (Attorney Docket No.ALA-009), entitled “INTELLIGENT NETWORK INTERFACE SYSTEM AND METHOD FORACCELERATED PROTOCOL PROCESSING”, filed Nov. 12, 1999, by Laurence B.Boucher et al., which in turn claims the benefit under 35 U.S.C. §120 ofU.S. patent application Ser. No. 09/067,544 (Attorney Docket No.ALA-002), entitled “INTELLIGENT NETWORK INTERFACE SYSTEM AND METHOD FORACCELERATED PROTOCOL PROCESSING”, filed Apr. 27, 1998, which in turnclaims the benefit under 35 U.S.C. § 1 19(e)(1) of the ProvisionalApplication filed under 35 U.S.C. §111(b) entitled “INTELLIGENT NETWORKINTERFACE CARD AND SYSTEM FOR PROTOCOL PROCESSING,” Serial No.60/061,809 (Attorney Docket No. ALA-001), filed on Oct. 14, 1997.

[0002] This application also claims the benefit under 35 U.S.C. §120 ofU.S. patent application Ser. No. 09/384,792 (Attorney Docket No.ALA-008), entitled “INTELLIGENT NETWORK INTERFACE DEVICE AND SYSTEM FORACCELERATED COMMUNICATION,” filed Aug. 27, 1999, which in turn claimsthe benefit under 35 U.S.C. §120 of U.S. patent application Ser. No.09/141,713 (Attorney Docket No. ALA-003), entitled “INTELLIGENT NETWORKINTERFACE DEVICE AND SYSTEM FOR ACCELERATED PROTOCOL PROCESSING”, filedAug. 28, 1998, which both claim the benefit under 35 U.S.C. § 119(e)(1)of the Provisional Application filed under 35 U.S.C. §111 (b) entitled“INTELLIGENT NETWORK INTERFACE DEVICE AND SYSTEM FOR ACCELERATEDCOMMUNICATION,” Serial No. 60/098,296 (Attorney Docket No. ALA-004),filed Aug. 27, 1998.

[0003] This application also claims the benefit under 35 U.S.C. §120 ofU.S. patent application Ser. No. 09/416,925 (Attorney Docket No.ALA-005), entitled “QUEUE SYSTEM FOR MICROPROCESSORS,” filed Oct. 13,1999, U.S. patent application Ser. No. 09/514,425 (Attorney Docket No.ALA-007), entitled “PROTOCOL PROCESSING STACK FOR USE WITH INTELLIGENTNETWORK INTERFACE CARD,” filed Feb. 28, 2000, U.S. patent applicationSer. No. 09/675,484 (Attorney Docket No. ALA-010A), entitled“INTELLIGENT NETWORK STORAGE INTERFACE SYSTEM,” filed Sep. 29, 2000,U.S. patent application Ser. No. 09/675,700 (Attorney Docket No.ALA-010B), entitled “INTELLIGENT NETWORK STORAGE INTERFACE DEVICE,”filed Sep. 29, 2000, U.S. patent application Ser. No. 09/789,366(Attorney Docket No. ALA-013), entitled “OBTAINING A DESTINATION ADDRESSSO THAT A NETWORK INTERFACE DEVICE CAN WRITE NETWORK DATA WITHOUTHEADERS DIRECTLY INTO HOST MEMORY,” filed Feb. 20, 2001, U.S. patentapplication Ser. No. 09/801,488 (Attorney Docket No. ALA-011), entitled“PORT AGGREGATION FOR NETWORK CONNECTIONS THAT ARE OFFLOADED TO NETWORKINTERFACE DEVICES,” filed Mar. 7, 2001, U.S. patent application Ser. No.09/802,551 (Attorney Docket No. ALA-012), entitled “INTELLIGENT NETWORKSTORAGE INTERFACE SYSTEM,” filed Mar. 9, 2001, U.S. patent applicationSer. No. 09/802,426 (Attorney Docket No. ALA-014), entitled “REDUCINGDELAYS ASSOCIATED WITH INSERTING A CHECKSUM INTO A NETWORK MESSAGE,”filed Mar. 9, 2001, U.S. patent application Ser. No. 09/802,550(Attorney Docket No. ALA-015), entitled “INTELLIGENT INTERFACE CARD ANDMETHOD FOR ACCELERATED PROTOCOL PROCESSING,” filed Mar. 9, 2001, U.S.patent application Ser. No. 09/855,979 (Attorney Docket No. ALA-016),entitled “NETWORK INTERFACE DEVICE EMPLOYING DMA COMMAND QUEUE,” filedMar. 14, 2001, U.S. patent application Ser. No. 09/970,124 (AttorneyDocket No. ALA-020), entitled “NETWORK INTERFACE DEVICE THAT FAST-PATHPROCESSES SOLICITED SESSION LAYER READ COMMANDS,” filed Oct. 2, 2001.

[0004] The subject matter of all of the above-identified patentapplications (including the subject matter in the Microfiche Appendix ofU.S. application Ser. No. 09/464,283), and of the two above-identifiedprovisional applications, is incorporated by reference herein.

REFERENCE TO COMPACT DISC APPENDIX

[0005] The Compact Disc Appendix (CD Appendix), which is a part of thepresent disclosure, includes three folders, designated CD Appendix A, CDAppendix B, and CD Appendix C on the compact disc. CD Appendix Acontains a hardware description language (verilog code) description ofan embodiment of a receive sequencer. CD Appendix B contains microcodeexecuted by a processor that operates in conjunction with the receivesequencer of CD Appendix A. CD Appendix C contains a device driverexecutable on the host as well as ATCP code executable on the host. Aportion of the disclosure of this patent document contains material(other than any portion of the “free BSD” stack included in CD AppendixC) which is subject to copyright protection. The copyright owner of thatmaterial has no objection to the facsimile reproduction by anyone of thepatent document or the patent disclosure, as it appears in the Patentand Trademark Office patent files or records, but otherwise reserves allcopyright rights.

TECHNICAL FIELD

[0006] The present invention relates generally to computer or othernetworks, and more particularly to processing of informationcommunicated between hosts such as computers connected to a network.

BACKGROUND

[0007] The advantages of network computing are increasingly evident. Theconvenience and efficiency of providing information, communication orcomputational power to individuals at their personal computer or otherend user devices has led to rapid growth of such network computing,including internet as well as intranet devices and applications.

[0008] As is well known, most network computer communication isaccomplished with the aid of a layered software architecture for movinginformation between host computers connected to the network. The layershelp to segregate information into manageable segments, the generalfunctions of each layer often based on an international standard calledOpen Systems Interconnection (OSI). OSI sets forth seven processinglayers through which information may pass when received by a host inorder to be presentable to an end user. Similarly, transmission ofinformation from a host to the network may pass through those sevenprocessing layers in reverse order. Each step of processing and serviceby a layer may include copying the processed information. Anotherreference model that is widely implemented, called TCP/IP (TCP standsfor transport control protocol, while IP denotes internet protocol)essentially employs five of the seven layers of OSI.

[0009] Networks may include, for instance, a high-speed bus such as anEthernet connection or an internet connection between disparate localarea networks (LANs), each of which includes multiple hosts, or any of avariety of other known means for data transfer between hosts. Accordingto the OSI standard, physical layers are connected to the network atrespective hosts, the physical layers providing transmission and receiptof raw data bits via the network. A data link layer is serviced by thephysical layer of each host, the data link layers providing framedivision and error correction to the data received from the physicallayers, as well as processing acknowledgment frames sent by thereceiving host. A network layer of each host is serviced by respectivedata link layers, the network layers primarily controlling size andcoordination of subnets of packets of data.

[0010] A transport layer is serviced by each network layer and a sessionlayer is serviced by each transport layer within each host. Transportlayers accept data from their respective session layers and split thedata into smaller units for transmission to the other host's transportlayer, which concatenates the data for presentation to respectivepresentation layers. Session layers allow for enhanced communicationcontrol between the hosts. Presentation layers are serviced by theirrespective session layers, the presentation layers translating betweendata semantics and syntax which may be peculiar to each host andstandardized structures of data representation. Compression and/orencryption of data may also be accomplished at the presentation level.Application layers are serviced by respective presentation layers, theapplication layers translating between programs particular to individualhosts and standardized programs for presentation to either anapplication or an end user. The TCP/IP standard includes the lower fourlayers and application layers, but integrates the functions of sessionlayers and presentation layers into adjacent layers. Generally speaking,application, presentation and session layers are defined as upperlayers, while transport, network and data link layers are defined aslower layers.

[0011] The rules and conventions for each layer are called the protocolof that layer, and since the protocols and general functions of eachlayer are roughly equivalent in various hosts, it is useful to think ofcommunication occurring directly between identical layers of differenthosts, even though these peer layers do not directly communicate withoutinformation transferring sequentially through each layer below. Eachlower layer performs a service for the layer immediately above it tohelp with processing the communicated information. Each layer saves theinformation for processing and service to the next layer. Due to themultiplicity of hardware and software architectures, devices andprograms commonly employed, each layer is necessary to insure that thedata can make it to the intended destination in the appropriate form,regardless of variations in hardware and software that may intervene.

[0012] In preparing data for transmission from a first to a second host,some control data is added at each layer of the first host regarding theprotocol of that layer, the control data being indistinguishable fromthe original (payload) data for all lower layers of that host. Thus anapplication layer attaches an application header to the payload data andsends the combined data to the presentation layer of the sending host,which receives the combined data, operates on it and adds a presentationheader to the data, resulting in another combined data packet. The dataresulting from combination of payload data, application header andpresentation header is then passed to the session layer, which performsrequired operations including attaching a session header to the data andpresenting the resulting combination of data to the transport layer.This process continues as the information moves to lower layers, with atransport header, network header and data link header and trailerattached to the data at each of those layers, with each step typicallyincluding data moving and copying, before sending the data as bitpackets over the network to the second host.

[0013] The receiving host generally performs the converse of theabove-described process, beginning with receiving the bits from thenetwork, as headers are removed and data processed in order from thelowest (physical) layer to the highest (application) layer beforetransmission to a destination of the receiving host. Each layer of thereceiving host recognizes and manipulates only the headers associatedwith that layer, since to that layer the higher layer control data isincluded with and indistinguishable from the payload data. Multipleinterrupts, valuable central processing unit (CPU) processing time andrepeated data copies may also be necessary for the receiving host toplace the data in an appropriate form at its intended destination.

[0014] The above description of layered protocol processing issimplified, as college-level textbooks devoted primarily to this subjectare available, such as Computer Networks, Third Edition (1996) by AndrewS. Tanenbaum, which is incorporated herein by reference. As defined inthat book, a computer network is an interconnected collection ofautonomous computers, such as internet and intranet devices, includinglocal area networks (LANs), wide area networks (WANs), asynchronoustransfer mode (ATM), ring or token ring, wired, wireless, satellite orother means for providing communication capability between separateprocessors. A computer is defined herein to include a device having bothlogic and memory functions for processing data, while computers or hostsconnected to a network are said to be heterogeneous if they functionaccording to different operating devices or communicate via differentarchitectures.

[0015] As networks grow increasingly popular and the informationcommunicated thereby becomes increasingly complex and copious, the needfor such protocol processing has increased. It is estimated that a largefraction of the processing power of a host CPU may be devoted tocontrolling protocol processes, diminishing the ability of that CPU toperform other tasks. Network interface cards have been developed to helpwith the lowest layers, such as the physical and data link layers. It isalso possible to increase protocol processing speed by simply addingmore processing power or CPUs according to conventional arrangements.This solution, however, is both awkward and expensive. But thecomplexities presented by various networks, protocols, architectures,operating devices and applications generally require extensiveprocessing to afford communication capability between various networkhosts.

SUMMARY OF THE INVENTION

[0016] The current invention provides a device for processing networkcommunication that greatly increases the speed of that processing andthe efficiency of transferring data being communicated. The inventionhas been achieved by questioning the long-standing practice ofperforming multilayered protocol processing on a general-purposeprocessor. The protocol processing method and architecture that resultseffectively collapses the layers of a connection-based, layeredarchitecture such as TCP/IP into a single wider layer which is able tosend network data more directly to and from a desired location or bufferon a host. This accelerated processing is provided to a host for bothtransmitting and receiving data, and so improves performance whether oneor both hosts involved in an exchange of information have such afeature.

[0017] The accelerated processing includes employing representativecontrol instructions for a given message that allow data from themessage to be processed via a fast-path which accesses message datadirectly at its source or delivers it directly to its intendeddestination. This fast-path bypasses conventional protocol processing ofheaders that accompany the data. The fast-path employs a specializedmicroprocessor designed for processing network communication, avoidingthe delays and pitfalls of conventional software layer processing, suchas repeated copying and interrupts to the CPU. In effect, the fast-pathreplaces the states that are traditionally found in several layers of aconventional network stack with a single state machine encompassing allthose layers, in contrast to conventional rules that require rigorousdifferentiation and separation of protocol layers. The host retains asequential protocol processing stack which can be employed for settingup a fast-path connection or processing message exceptions. Thespecialized microprocessor and the host intelligently choose whether agiven message or portion of a message is processed by the microprocessoror the host stack.

[0018] One embodiment is a method of generating a fast-path response toa packet received onto a network interface device where the packet isreceived over a TCP/IP network connection and where the TCP/IP networkconnection is identified at least in part by a TCP source port, a TCPdestination port, an IP source address, and an IP destination address.The method comprises: 1) Examining the packet and determining from thepacket the TCP source port, the TCP destination port, the IP sourceaddress, and the IP destination address; 2) Accessing an appropriatetemplate header stored on the network interface device. The templateheader has TCP fields and IP fields; 3) Employing a finite state machinethat implements both TCP protocol processing and IP protocol processingto fill in the TCP fields and IP fields of the template header; and 4)Transmitting the fast-path response from the network interface device.The fast-path response includes the filled in template header and apayload. The finite state machine does not entail a TCP protocolprocessing layer and a discrete IP protocol processing layer where theTCP and IP layers are executed one after another in sequence. Rather,the finite state machine covers both TCP and IP protocol processinglayers.

[0019] In one embodiment, buffer descriptors that point to packets to betransmitted are pushed onto a plurality of transmit queues. A transmitsequencer pops the transmit queues and obtains the buffer descriptors.The buffer descriptors are then used to retrieve the packets frombuffers where the packets are stored. The retrieved packets are thentransmitted from the network interface device. In one embodiment, thereare two transmit queues, one having a higher transmission priority thanthe other. Packets identified by buffer descriptors on the higherpriority transmit queue are transmitted from the network interfacedevice before packets identified by the lower priority transmit queue.

[0020] Other structures and methods are disclosed in the detaileddescription below. This summary does not purport to define theinvention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a plan view diagram of a device of the presentinvention, including a host computer having a communication-processingdevice for accelerating network communication.

[0022]FIG. 2 is a diagram of information flow for the host of FIG. 1 inprocessing network communication, including a fast-path, a slow-path anda transfer of connection context between the fast and slow-paths.

[0023]FIG. 3 is a flow chart of message receiving according to thepresent invention.

[0024]FIG. 4A is a diagram of information flow for the host of FIG. 1receiving a message packet processed by the slow-path.

[0025]FIG. 4B is a diagram of information flow for the host of FIG. 1receiving an initial message packet processed by the fast-path.

[0026]FIG. 4C is a diagram of information flow for the host of FIG. 4Breceiving a subsequent message packet processed by the fast-path.

[0027]FIG. 4D is a diagram of information flow for the host of FIG. 4Creceiving a message packet having an error that causes processing torevert to the slow-path.

[0028]FIG. 5 is a diagram of information flow for the host of FIG. 1transmitting a message by either the fast or slow-paths.

[0029]FIG. 6 is a diagram of information flow for a first embodiment ofan intelligent network interface card (INIC) associated with a clienthaving a TCP/IP processing stack.

[0030]FIG. 7 is a diagram of hardware logic for the INIC embodimentshown in FIG. 6, including a packet control sequencer and a fly-bysequencer.

[0031]FIG. 8 is a diagram of the fly-by sequencer of FIG. 7 foranalyzing header bytes as they are received by the INIC.

[0032]FIG. 9 is a diagram of information flow for a second embodiment ofan INIC associated with a server having a TCP/IP processing stack.

[0033]FIG. 10 is a diagram of a command driver installed in the host ofFIG. 9 for creating and controlling a communication control block forthe fast-path.

[0034]FIG. 11 is a diagram of the TCP/IP stack and command driver ofFIG. 10 configured for NetBios communications.

[0035]FIG. 12 is a diagram of a communication exchange between theclient of FIG. 6 and the server of FIG. 9.

[0036]FIG. 13 is a diagram of hardware functions included in the INIC ofFIG. 9.

[0037]FIG. 14 is a diagram of a trio of pipelined microprocessorsincluded in the INIC of FIG. 13, including three phases with a processorin each phase.

[0038]FIG. 15A is a diagram of a first phase of the pipelinedmicroprocessor of FIG. 14.

[0039]FIG. 15B is a diagram of a second phase of the pipelinedmicroprocessor of FIG. 14.

[0040]FIG. 15C is a diagram of a third phase of the pipelinedmicroprocessor of FIG. 14.

[0041]FIG. 16 is a diagram of a plurality of queue storage units thatinteract with the microprocessor of FIG. 14 and include SRAM and DRAM.

[0042]FIG. 17 is a diagram of a set of status registers for the queuesstorage units of FIG. 16.

[0043]FIG. 18 is a diagram of a queue manager, which interacts, with thequeue storage units and status registers of FIG. 16 and FIG. 17.

[0044] FIGS. 19A-D are diagrams of various stages of aleast-recently-used register that is employed for allocating cachememory.

[0045]FIG. 20 is a diagram of the devices used to operate theleast-recently-used register of FIGS. 19A-D.

[0046]FIG. 21 is another diagram of Intelligent Network Interface Card(INIC) 200 of FIG. 13.

[0047]FIG. 22 is a diagram of the receive sequencer of FIG. 21.

[0048]FIG. 23 is a diagram illustrating a “fast-path” transfer of dataof a multi-packet message from INIC 200 to a destination 2311 in host20.

[0049] FIGS. 24-107 are associated with the description below entitled“Disclosure From Provisional Application No. 60/061,809.”

DETAILED DESCRIPTION

[0050]FIG. 1 shows a host 20 of the present invention connected by anetwork 25 to a remote host 22. The increase in processing speedachieved by the present invention can be provided with an intelligentnetwork interface card (INIC) that is easily and affordably added to anexisting host, or with a communication processing device (CPD) that isintegrated into a host, in either case freeing the host CPU from mostprotocol processing and allowing improvements in other tasks performedby that CPU. The host 20 in a first embodiment contains a CPU 28 and aCPD 30 connected by a host bus 33. The CPD 30 includes a microprocessordesigned for processing communication data and memory buffers controlledby a direct memory access (DMA) unit. Also connected to the host bus 33is a storage device 35, such as a semiconductor memory or disk drive,along with any related controls.

[0051] Referring additionally to FIG. 2, the host CPU 28 controls aprotocol processing stack 44 housed in storage 35, the stack including adata link layer 36, network layer 38, transport layer 40, upper layer 46and an upper layer interface 42. The upper layer 46 may represent asession, presentation and/or application layer, depending upon theparticular protocol being employed and message communicated. The upperlayer interface 42, along with the CPU 28 and any related controls cansend or retrieve a file to or from the upper layer 46 or storage 35, asshown by arrow 48. A connection context 50 has been created, as will beexplained below, the context summarizing various features of theconnection, such as protocol type and source and destination addressesfor each protocol layer. The context may be passed between an interfacefor the session layer 42 and the CPD 30, as shown by arrows 52 and 54,and stored as a communication control block (CCB) at either CPD 30 orstorage 35.

[0052] When the CPD 30 holds a CCB defining a particular connection,data received by the CPD from the network and pertaining to theconnection is referenced to that CCB and can then be sent directly tostorage 35 according to a fast-path 58, bypassing sequential protocolprocessing by the data link 36, network 38 and transport 40 layers.Transmitting a message, such as sending a file from storage 35 to remotehost 22, can also occur via the fast-path 58, in which case the contextfor the file data is added by the CPD 30 referencing a CCB, rather thanby sequentially adding headers during processing by the transport 40,network 38 and data link 36 layers. The DMA controllers of the CPD 30perform these transfers between CPD and storage 35.

[0053] The CPD 30 collapses multiple protocol stacks each havingpossible separate states into a single state machine for fast-pathprocessing. As a result, exception conditions may occur that are notprovided for in the single state machine, primarily because suchconditions occur infrequently and to deal with them on the CPD wouldprovide little or no performance benefit to the host. Such exceptionscan be CPD 30 or CPU 28 initiated. An advantage of the inventionincludes the manner in which unexpected situations that occur on afast-path CCB are handled. The CPD 30 deals with these rare situationsby passing back or flushing to the host protocol stack 44 the CCB andany associated message frames involved, via a control negotiation. Theexception condition is then processed in a conventional manner by thehost protocol stack 44. At some later time, usually directly after thehandling of the exception condition has completed and fast-pathprocessing can resume, the host stack 44 hands the CCB back to the CPD.

[0054] This fallback capability enables the performance-impactingfunctions of the host protocols to be handled by the CPD networkmicroprocessor, while the exceptions are dealt with by the host stacks,the exceptions being so rare as to negligibly effect overallperformance. The custom designed network microprocessor can haveindependent processors for transmitting and receiving networkinformation, and further processors for assisting and queuing. Apreferred microprocessor embodiment includes a pipelined trio ofreceive, transmit and utility processors. DMA controllers are integratedinto the implementation and work in close concert with the networkmicroprocessor to quickly move data between buffers adjacent to thecontrollers and other locations such as long term storage. Providingbuffers logically adjacent to the DMA controllers avoids unnecessaryloads on the PCI bus.

[0055]FIG. 3 diagrams the general flow of messages received according tothe current invention. A large TCP/IP message such as a file transfermay be received by the host from the network in a number of separate,approximately 64 KB transfers, each of which may be split into many,approximately 1.5 KB frames or packets for transmission over a network.Novell NetWare protocol suites running Sequenced Packet ExchangeProtocol (SPX) or NetWare Core Protocol (NCP) over Internetwork PacketExchange (IPX) work in a similar fashion. Another form of datacommunication which can be handled by the fast-path is Transaction TCP(hereinafter T/TCP or TTCP), a version of TCP which initiates aconnection with an initial transaction request after which a replycontaining data may be sent according to the connection, rather thaninitiating a connection via a several-message initialization dialogueand then transferring data with later messages. In any of the transferstypified by these protocols, each packet conventionally includes aportion of the data being transferred, as well as headers for each ofthe protocol layers and markers for positioning the packet relative tothe rest of the packets of this message.

[0056] When a message packet or frame is received 47 from a network bythe CPD, it is first validated by a hardware assist. This includesdetermining the protocol types of the various layers, verifying relevantchecksums, and summarizing 57 these findings into a status word orwords. Included in these words is an indication whether or not the frameis a candidate for fast-path data flow. Selection 59 of fast-pathcandidates is based on whether the host may benefit from this messageconnection being handled by the CPD, which includes determining whetherthe packet has header bytes indicating particular protocols, such asTCP/IP or SPX/IPX for example. The small percent of frames that are notfast-path candidates are sent 61 to the host protocol stacks forslow-path protocol processing. Subsequent network microprocessor workwith each fast-path candidate determines whether a fast-path connectionsuch as a TCP or SPX CCB is already extant for that candidate, orwhether that candidate may be used to set up a new fast-path connection,such as for a TTCP/IP transaction. The validation provided by the CPDprovides acceleration whether a frame is processed by the fast-path or aslow-path, as only error free, validated frames are processed by thehost CPU even for the slow-path processing.

[0057] All received message frames which have been determined by the CPDhardware assist to be fast-path candidates are examined 53 by thenetwork microprocessor or INIC comparator circuits to determine whetherthey match a CCB held by the CPD. Upon confirming such a match, the CPDremoves lower layer headers and sends 69 the remaining application datafrom the frame directly into its final destination in the host usingdirect memory access (DMA) units of the CPD. This operation may occurimmediately upon receipt of a message packet, for example when a TCPconnection already exists and destination buffers have been negotiated,or it may first be necessary to process an initial header to acquire anew set of final destination addresses for this transfer. In this lattercase, the CPD will queue subsequent message packets while waiting forthe destination address, and then DMA the queued application data tothat destination.

[0058] A fast-path candidate that does not match a CCB may be used toset up a new fast-path connection, by sending 65 the frame to the hostfor sequential protocol processing. In this case, the host uses thisframe to create 51 a CCB, which is then passed to the CPD to controlsubsequent frames on that connection. The CCB, which is cached 67 in theCPD, includes control and state information pertinent to all protocolsthat would have been processed had conventional software layerprocessing been employed. The CCB also contains storage space forper-transfer information used to facilitate moving application-leveldata contained within subsequent related message packets directly to ahost application in a form available for immediate usage. The CPD takescommand of connection processing upon receiving a CCB for thatconnection from the host.

[0059] As shown more specifically in FIG. 4A, when a message packet isreceived from the remote host 22 via network 25, the packet entershardware receive logic 32 of the CPD 30, which checksums headers anddata, and parses the headers, creating a word or words which identifythe message packet and status, storing the headers, data and wordtemporarily in memory 60. As well as validating the packet, the receivelogic 32 indicates with the word whether this packet is a candidate forfast-path processing. FIG. 4A depicts the case in which the packet isnot a fast-path candidate, in which case the CPD 30 sends the validatedheaders and data from memory 60 to data link layer 36 along an internalbus for processing by the host CPU, as shown by arrow 56. The packet isprocessed by the host protocol stack 44 of data link 36, network 38,transport 40 and session 42 layers, and data (D) 63 from the packet maythen be sent to storage 35, as shown by arrow 65.

[0060]FIG. 4B, depicts the case in which the receive logic 32 of the CPDdetermines that a message packet is a candidate for fast-pathprocessing, for example by deriving from the packet's headers that thepacket belongs to a TCP/IP, TTCP/IP or SPX/IPX message. A processor 55in the CPD 30 then checks to see whether the word that summarizes thefast-path candidate matches a CCB held in a cache 62. Upon finding nomatch for this packet, the CPD sends the validated packet from memory 60to the host protocol stack 44 for processing. Host stack 44 may use thispacket to create a connection context for the message, including findingand reserving a destination for data from the message associated withthe packet, the context taking the form of a CCB. The present embodimentemploys a single specialized host stack 44 for processing both fast-pathand non-fast-path candidates, while in an embodiment described belowfast-path candidates are processed by a different host stack thannon-fast-path candidates. Some data (D1) 66 from that initial packet mayoptionally be sent to the destination in storage 35, as shown by arrow68. The CCB is then sent to the CPD 30 to be saved in cache 62, as shownby arrow 64. For a traditional connection-based message such as typifiedby TCP/IP, the initial packet may be part of a connection initializationdialogue that transpires between hosts before the CCB is created andpassed to the CPD 30.

[0061] Referring now to FIG. 4C, when a subsequent packet from the sameconnection as the initial packet is received from the network 25 by CPD30, the packet headers and data are validated by the receive logic 32,and the headers are parsed to create a summary of the message packet anda hash for finding a corresponding CCB, the summary and hash containedin a word or words. The word or words are temporarily stored in memory60 along with the packet. The processor 55 checks for a match betweenthe hash and each CCB that is stored in the cache 62 and, finding amatch, sends the data (D2) 70 via a fast-path directly to thedestination in storage 35, as shown by arrow 72, bypassing the sessionlayer 42, transport layer 40, network layer 38 and data link layer 36.The remaining data packets from the message can also be sent by DMAdirectly to storage, avoiding the relatively slow protocol layerprocessing and repeated copying by the CPU stack 44.

[0062]FIG. 4D shows the procedure for handling the rare instance when amessage for which a fast-path connection has been established, such asshown in FIG. 4C, has a packet that is not easily handled by the CPD. Inthis case the packet is sent to be processed by the protocol stack 44,which is handed the CCB for that message from cache 62 via a controldialogue with the CPD, as shown by arrow 76, signaling to the CPU totake over processing of that message. Slow-path processing by theprotocol stack then results in data (D3) 80 from the packet being sent,as shown by arrow 82, to storage 35. Once the packet has been processedand the error situation corrected, the CCB can be handed back via acontrol dialogue to the cache 62, so that payload data from subsequentpackets of that message can again be sent via the fast-path of the CPD30. Thus the CPU and CPD together decide whether a given message is tobe processed according to fast-path hardware processing or moreconventional software processing by the CPU.

[0063] Transmission of a message from the host 20 to the network 25 fordelivery to remote host 22 also can be processed by either sequentialprotocol software processing via the CPU or accelerated hardwareprocessing via the CPD 30, as shown in FIG. 5. A message (M) 90 that isselected by CPU 28 from storage 35 can be sent to session layer 42 forprocessing by stack 44, as shown by arrows 92 and 96. For the situationin which a connection exists and the CPD 30 already has an appropriateCCB for the message, however, data packets can bypass host stack 44 andbe sent by DMA directly to memory 60, with the processor 55 adding toeach data packet a single header containing all the appropriate protocollayers, and sending the resulting packets to the network 25 fortransmission to remote host 22. This fast-path transmission can greatlyaccelerate processing for even a single packet, with the accelerationmultiplied for a larger message.

[0064] A message for which a fast-path connection is not extant thus maybenefit from creation of a CCB with appropriate control and stateinformation for guiding fast-path transmission. For a traditionalconnection-based message, such as typified by TCP/IP or SPX/IPX, the CCBis created during connection initialization dialogue. For aquick-connection message, such as typified by TTCP/IP, the CCB can becreated with the same transaction that transmits payload data. In thiscase, the transmission of payload data may be a reply to a request thatwas used to set up the fast-path connection. In any case, the CCBprovides protocol and status information regarding each of the protocollayers, including which user is involved and storage space forper-transfer information. The CCB is created by protocol stack 44, whichthen passes the CCB to the CPD 30 by writing to a command register ofthe CPD, as shown by arrow 98. Guided by the CCB, the processor 55 movesnetwork frame-sized portions of the data from the source in host memory35 into its own memory 60 using DMA, as depicted by arrow 99. Theprocessor 55 then prepends appropriate headers and checksums to the dataportions, and transmits the resulting frames to the network 25,consistent with the restrictions of the associated protocols. After theCPD 30 has received an acknowledgement that all the data has reached itsdestination, the CPD will then notify the host 35 by writing to aresponse buffer. Thus, fast-path transmission of data communicationsalso relieves the host CPU of per-frame processing. A vast majority ofdata transmissions can be sent to the network by the fast-path. Both theinput and output fast-paths attain a huge reduction in interrupts byfunctioning at an upper layer level, i.e., session level or higher, andinteractions between the network microprocessor and the host occur usingthe full transfer sizes which that upper layer wishes to make. Forfast-path communications, an interrupt only occurs (at the most) at thebeginning and end of an entire upper-layer message transaction, andthere are no interrupts for the sending or receiving of each lower layerportion or packet of that transaction.

[0065] A simplified intelligent network interface card (INIC) 150 isshown in FIG. 6 to provide a network interface for a host 152. Hardwarelogic 171 of the INIC 150 is connected to a network 155, with aperipheral bus (PCI) 157 connecting the INIC and host. The host 152 inthis embodiment has a TCP/IP protocol stack, which provides a slow-path158 for sequential software processing of message frames received fromthe network 155. The host 152 protocol stack includes a data link layer160, network layer 162, a transport layer 164 and an application layer166, which provides a source or destination 168 for the communicationdata in the host 152. Other layers which are not shown, such as sessionand presentation layers, may also be included in the host stack 152, andthe source or destination may vary depending upon the nature of the dataand may actually be the application layer.

[0066] The INIC 150 has a network processor 170 which chooses betweenprocessing messages along a slow-path 158 that includes the protocolstack of the host, or along a fast-path 159 that bypasses the protocolstack of the host. Each received packet is processed on the fly byhardware logic 171 contained in INIC 150, so that all of the protocolheaders for a packet can be processed without copying, moving or storingthe data between protocol layers. The hardware logic 171 processes theheaders of a given packet at one time as packet bytes pass through thehardware, by categorizing selected header bytes. Results of processingthe selected bytes help to determine which other bytes of the packet arecategorized, until a summary of the packet has been created, includingchecksum validations. The processed headers and data from the receivedpacket are then stored in INIC storage 185, as well as the word or wordssummarizing the headers and status of the packet. For a network storageconfiguration, the INIC 150 may be connected to a peripheral storagedevice such as a disk drive which has an IDE, SCSI or similar interface,with a file cache for the storage device residing on the memory 185 ofthe INIC 150. Several such network interfaces may exist for a host, witheach interface having an associated storage device.

[0067] The hardware processing of message packets received by INIC 150from network 155 is shown in more detail in FIG. 7. A received messagepacket first enters a media access controller 172, which controls INICaccess to the network and receipt of packets and can provide statisticalinformation for network protocol management. From there, data flows onebyte at a time into an assembly register 174, which in this example is128 bits wide. The data is categorized by a fly-by sequencer 178, aswill be explained in more detail with regard to FIG. 8, which examinesthe bytes of a packet as they fly by, and generates status from thosebytes that will be used to summarize the packet. The status thus createdis merged with the data by a multiplexor 180 and the resulting datastored in SRAM 182. A packet control sequencer 176 oversees the fly-bysequencer 178, examines information from the media access controller172, counts the bytes of data, generates addresses, moves status andmanages the movement of data from the assembly register 174 to SRAM 182and eventually DRAM 188. The packet control sequencer 176 manages abuffer in SRAM 182 via SRAM controller 183, and also indicates to a DRAMcontroller 186 when data needs to be moved from SRAM 182 to a buffer inDRAM 188. Once data movement for the packet has been completed and allthe data has been moved to the buffer in DRAM 188, the packet controlsequencer 176 will move the status that has been generated in the fly-bysequencer 178 out to the SRAM 182 and to the beginning of the DRAM 188buffer to be prepended to the packet data. The packet control sequencer176 then requests a queue manager 184 to enter a receive bufferdescriptor into a receive queue, which in turn notifies the processor170 that the packet has been processed by hardware logic 171 and itsstatus summarized.

[0068]FIG. 8 shows that the fly-by sequencer 178 has several tiers, witheach tier generally focusing on a particular portion of the packetheader and thus on a particular protocol layer, for generating statuspertaining to that layer. The fly-by sequencer 178 in this embodimentincludes a media access control sequencer 191, a network sequencer 192,a transport sequencer 194 and a session sequencer 195. Sequencerspertaining to higher protocol layers can additionally be provided. Thefly-by sequencer 178 is reset by the packet control sequencer 176 andgiven pointers by the packet control sequencer that tell the fly-bysequencer whether a given byte is available from the assembly register174. The media access control sequencer 191 determines, by looking atbytes 0-5, that a packet is addressed to host 152 rather than or inaddition to another host. Offsets 12 and 13 of the packet are alsoprocessed by the media access control sequencer 191 to determine thetype field, for example whether the packet is Ethernet or 802.3. If thetype field is Ethernet those bytes also tell the media access controlsequencer 191 the packet's network protocol type. For the 802.3 case,those bytes instead indicate the length of the entire frame, and themedia access control sequencer 191 will check eight bytes further intothe packet to determine the network layer type.

[0069] For most packets the network sequencer 192 validates that theheader length received has the correct length, and checksums the networklayer header. For fast-path candidates the network layer header is knownto be IP or IPX from analysis done by the media access control sequencer191. Assuming for example that the type field is 802.3 and the networkprotocol is IP, the network sequencer 192 analyzes the first bytes ofthe network layer header, which will begin at byte 22, in order todetermine IP type. The first bytes of the IP header will be processed bythe network sequencer 192 to determine what IP type the packet involves.Determining that the packet involves, for example, IP version 4, directsfurther processing by the network sequencer 192, which also looks at theprotocol type located ten bytes into the IP header for an indication ofthe transport header protocol of the packet. For example, for IP overEthernet, the IP header begins at offset 14, and the protocol type byteis offset 23, which will be processed by network logic to determinewhether the transport layer protocol is TCP, for example. From thelength of the network layer header, which is typically 20-40 bytes,network sequencer 192 determines the beginning of the packet's transportlayer header for validating the transport layer header. Transportsequencer 194 may generate checksums for the transport layer header anddata, which may include information from the IP header in the case ofTCP at least.

[0070] Continuing with the example of a TCP packet, transport sequencer194 also analyzes the first few bytes in the transport layer portion ofthe header to determine, in part, the TCP source and destination portsfor the message, such as whether the packet is NetBios or otherprotocols. Byte 12 of the TCP header is processed by the transportsequencer 194 to determine and validate the TCP header length. Byte 13of the TCP header contains flags that may, aside from ack flags and pushflags, indicate unexpected options, such as reset and fin, that maycause the processor to categorize this packet as an exception. TCPoffset bytes 16 and 17 are the checksum, which is pulled out and storedby the hardware logic 171 while the rest of the frame is validatedagainst the checksum.

[0071] Session sequencer 195 determines the length of the session layerheader, which in the case of NetBios is only four bytes, two of whichtell the length of the NetBios payload data, but which can be muchlarger for other protocols. The session sequencer 195 can also be usedto categorize the type of message as read or write, for example, forwhich the fast-path may be particularly beneficial. Further upper layerlogic processing, depending upon the message type, can be performed bythe hardware logic 171 of packet control sequencer 176 and fly-bysequencer 178. Thus hardware logic 171 intelligently directs hardwareprocessing of the headers by categorization of selected bytes from asingle stream of bytes, with the status of the packet being built fromclassifications determined on the fly. Once the packet control sequencer176 detects that all of the packet has been processed by the fly-bysequencer 178, the packet control sequencer 176 adds the statusinformation generated by the fly-by sequencer 178 and any statusinformation generated by the packet control sequencer 176, and prepends(adds to the front) that status information to the packet, forconvenience in handling the packet by the processor 170. The additionalstatus information generated by the packet control sequencer 176includes media access controller 172 status information and any errorsdiscovered, or data overflow in either the assembly register or DRAMbuffer, or other miscellaneous information regarding the packet. Thepacket control sequencer 176 also stores entries into a receive bufferqueue and a receive statistics queue via the queue manager 184. Anadvantage of processing a packet by hardware logic 171 is that thepacket does not, in contrast with conventional sequential softwareprotocol processing, have to be stored, moved, copied or pulled fromstorage for processing each protocol layer header, offering dramaticincreases in processing efficiency and savings in processing time foreach packet. The packets can be processed at the rate bits are receivedfrom the network, for example 100 megabits/second for a 100 baseTconnection. The time for categorizing a packet received at this rate andhaving a length of sixty bytes is thus about 5 microseconds. The totaltime for processing this packet with the hardware logic 171 and sendingpacket data to its host destination via the fast-path may be about 16microseconds or less, assuming a 66 MHz PCI bus, whereas conventionalsoftware protocol processing by a 300 MHz Pentium II® processor may takeas much as 200 microseconds in a busy device. More than an order ofmagnitude decrease in processing time can thus be achieved withfast-path 159 in comparison with a high-speed CPU employing conventionalsequential software protocol processing, demonstrating the dramaticacceleration provided by processing the protocol headers by the hardwarelogic 171 and processor 170, without even considering the additionaltime savings afforded by the reduction in CPU interrupts and host busbandwidth savings.

[0072] The processor 170 chooses, for each received message packet heldin storage 185, whether that packet is a candidate for the fast-path 159and, if so, checks to see whether a fast-path has already been set upfor the connection that the packet belongs to. To do this, the processor170 first checks the header status summary to determine whether thepacket headers are of a protocol defined for fast-path candidates. Ifnot, the processor 170 commands DMA controllers in the INIC 150 to sendthe packet to the host for slow-path 158 processing. Even for aslow-path 158 processing of a message, the INIC 150 thus performsinitial procedures such as validation and determination of message type,and passes the validated message at least to the data link layer 160 ofthe host.

[0073] For fast-path 159 candidates, the processor 170 checks to seewhether the header status summary matches a CCB held by the INIC. If so,the data from the packet is sent along fast-path 159 to the destination168 in the host. If the fast-path 159 candidate's packet summary doesnot match a CCB held by the INIC, the packet may be sent to the host 152for slow-path processing to create a CCB for the message. Employment ofthe fast-path 159 may also not be needed or desirable for the case offragmented messages or other complexities. For the vast majority ofmessages, however, the INIC fast-path 159 can greatly accelerate messageprocessing. The INIC 150 thus provides a single state machine processor170 that decides whether to send data directly to its destination, basedupon information gleaned on the fly, as opposed to the conventionalemployment of a state machine in each of several protocol layers fordetermining the destiny of a given packet.

[0074] In processing an indication or packet received at the host 152, aprotocol driver of the host selects the processing route based uponwhether the indication is fast-path or slow-path. A TCP/IP or SPX/IPXmessage has a connection that is set up from which a CCB is formed bythe driver and passed to the INIC for matching with and guiding thefast-path packet to the connection destination 168. For a TTCP/IPmessage, the driver can create a connection context for the transactionfrom processing an initial request packet, including locating themessage destination 168, and then passing that context to the INIC inthe form of a CCB for providing a fast-path for a reply from thatdestination. A CCB includes connection and state information regardingthe protocol layers and packets of the message. Thus a CCB can includesource and destination media access control (MAC) addresses, source anddestination IP or IPX addresses, source and destination TCP or SPXports, TCP variables such as timers, receive and transmit windows forsliding window protocols, and information indicating the session layerprotocol.

[0075] Caching the CCBs in a hash table in the INIC provides quickcomparisons with words summarizing incoming packets to determine whetherthe packets can be processed via the fast-path 159, while the full CCBsare also held in the INIC for processing. Other ways to accelerate thiscomparison include software processes such as a B-tree or hardwareassists such as a content addressable memory (CAM). When INIC microcodeor comparator circuits detect a match with the CCB, a DMA controllerplaces the data from the packet in the destination 168, without anyinterrupt by the CPU, protocol processing or copying. Depending upon thetype of message received, the destination of the data may be thesession, presentation or application layers, or a file buffer cache inthe host 152.

[0076]FIG. 9 shows an INIC 200 connected to a host 202 that is employedas a file server. This INIC provides a network interface for severalnetwork connections employing the 802.3 u standard, commonly known asFast Ethernet. The INIC 200 is connected by a PCI bus 205 to the server202, which maintains a TCP/IP or SPX/IPX protocol stack including MAClayer 212, network layer 215, transport layer 217 and application layer220, with a source/destination 222 shown above the application layer,although as mentioned earlier the application layer can be the source ordestination. The INIC is also connected to network lines 210, 240, 242and 244, which are preferably Fast Ethernet, twisted pair, fiber optic,coaxial cable or other lines each allowing data transmission of 100Mb/s, while faster and slower data rates are also possible. Networklines 210, 240, 242 and 244 are each connected to a dedicated row ofhardware circuits which can each validate and summarize message packetsreceived from their respective network line. Thus line 210 is connectedwith a first horizontal row of sequencers 250, line 240 is connectedwith a second horizontal row of sequencers 260, line 242 is connectedwith a third horizontal row of sequencers 262 and line 244 is connectedwith a fourth horizontal row of sequencers 264. After a packet has beenvalidated and summarized by one of the horizontal hardware rows it isstored along with its status summary in storage 270.

[0077] A network processor 230 determines, based on that summary and acomparison with any CCBs stored in the INIC 200, whether to send apacket along a slow-path 231 for processing by the host. A largemajority of packets can avoid such sequential processing and have theirdata portions sent by DMA along a fast-path 237 directly to the datadestination 222 in the server according to a matching CCB. Similarly,the fast-path 237 provides an avenue to send data directly from thesource 222 to any of the network lines by processor 230 division of thedata into packets and addition of full headers for network transmission,again minimizing CPU processing and interrupts. For clarity onlyhorizontal sequencer 250 is shown active; in actuality each of thesequencer rows 250, 260, 262 and 264 offers full duplex communication,concurrently with all other sequencer rows. The specialized INIC 200 ismuch faster at working with message packets than even advancedgeneral-purpose host CPUs that processes those headers sequentiallyaccording to the software protocol stack.

[0078] One of the most commonly used network protocols for largemessages such as file transfers is server message block (SMB) overTCP/IP. SMB can operate in conjunction with redirector software thatdetermines whether a required resource for a particular operation, suchas a printer or a disk upon which a file is to be written, resides in oris associated with the host from which the operation was generated or islocated at another host connected to the network, such as a file server.SMB and server/redirector are conventionally serviced by the transportlayer; in the present invention SMB and redirector can instead beserviced by the INIC. In this case, sending data by the DMA controllersfrom the INIC buffers when receiving a large SMB transaction may greatlyreduce interrupts that the host must handle. Moreover, this DMAgenerally moves the data to its final destination in the file devicecache. An SMB transmission of the present invention follows essentiallythe reverse of the above described SMB receive, with data transferredfrom the host to the INIC and stored in buffers, while the associatedprotocol headers are prepended to the data in the INIC, for transmissionvia a network line to a remote host. Processing by the INIC of themultiple packets and multiple TCP, IP, NetBios and SMB protocol layersvia custom hardware and without repeated interrupts of the host cangreatly increase the speed of transmitting an SMB message to a networkline.

[0079] As shown in FIG. 10, for controlling whether a given message isprocessed by the host 202 or by the INIC 200, a message command driver300 may be installed in host 202 to work in concert with a host protocolstack 310. The command driver 300 can intervene in message reception ortransmittal, create CCBs and send or receive CCBs from the INIC 200, sothat functioning of the INIC, aside from improved performance, istransparent to a user. Also shown is an INIC memory 304 and an INICminiport driver 306, which can direct message packets received fromnetwork 210 to either the conventional protocol stack 310 or the commandprotocol stack 300, depending upon whether a packet has been labeled asa fast-path candidate. The conventional protocol stack 310 has a datalink layer 312, a network layer 314 and a transport layer 316 forconventional, lower layer processing of messages that are not labeled asfast-path candidates and therefore not processed by the command stack300. Residing above the lower layer stack 310 is an upper layer 318,which represents a session, presentation and/or application layer,depending upon the message communicated. The command driver 300similarly has a data link layer 320, a network layer 322 and a transportlayer 325.

[0080] The driver 300 includes an upper layer interface 330 thatdetermines, for transmission of messages to the network 210, whether amessage transmitted from the upper layer 318 is to be processed by thecommand stack 300 and subsequently the INIC fast-path, or by theconventional stack 310. When the upper layer interface 330 receives anappropriate message from the upper layer 318 that would conventionallybe intended for transmission to the network after protocol processing bythe protocol stack of the host, the message is passed to driver 300. TheINIC then acquires network-sized portions of the message data for thattransmission via INIC DMA units, prepends headers to the data portionsand sends the resulting message packets down the wire. Conversely, inreceiving a TCP, TTCP, SPX or similar message packet from the network210 to be used in setting up a fast-path connection, miniport driver 306diverts that message packet to command driver 300 for processing. Thedriver 300 processes the message packet to create a context for thatmessage, with the driver 302 passing the context and commandinstructions back to the INIC 200 as a CCB for sending data ofsubsequent messages for the same connection along a fast-path. Hundredsof TCP, TTCP, SPX or similar CCB connections may be held indefinitely bythe INIC, although a least recently used (LRU) algorithm is employed forthe case when the INIC cache is full. The driver 300 can also create aconnection context for a TTCP request which is passed to the INIC 200 asa CCB, allowing fast-path transmission of a TTCP reply to the request. Amessage having a protocol that is not accelerated can be processedconventionally by protocol stack 310.

[0081]FIG. 11 shows a TCP/IP implementation of command driver softwarefor Microsoft® protocol messages. A conventional host protocol stack 350includes MAC layer 353, IP layer 355 and TCP layer 358. A command driver360 works in concert with the host stack 350 to process networkmessages. The command driver 360 includes a MAC layer 363, an IP layer366 and an Alacritech TCP (ATCP) layer 373. The conventional stack 350and command driver 360 share a network driver interface specification(NDIS) layer 375, which interacts with the INIC miniport driver 306. TheINIC miniport driver 306 sorts receive indications for processing byeither the conventional host stack 350 or the ATCP driver 360. A TDIfilter driver and upper layer interface 380 similarly determines whethermessages sent from a TDI user 382 to the network are diverted to thecommand driver and perhaps to the fast-path of the INIC, or processed bythe host stack.

[0082]FIG. 12 depicts a typical SMB exchange between a client 190 andserver 290, both of which have communication devices of the presentinvention, the communication devices each holding a CCB defining theirconnection for fast-path movement of data. The client 190 includes INIC150, 802.3 compliant data link layer 160, IP layer 162, TCP layer 164,NetBios layer 166, and SMB layer 168. The client has a slow-path 157 andfast-path 159 for communication processing. Similarly, the server 290includes INIC 200, 802.3 compliant data link layer 212, IP layer 215,TCP layer 217, NetBios layer 220, and SMB 222. The server is connectedto network lines 240, 242 and 244, as well as line 210 which isconnected to client 190. The server also has a slow-path 231 andfast-path 237 for communication processing. Assuming that the client 190wishes to read a 100 KB file on the server 290, the client may begin bysending a Read Block Raw (RBR) SMB command across network 210 requestingthe first 64 KB of that file on the server 290. The RBR command may beonly 76 bytes, for example, so the INIC 200 on the server will recognizethe message type (SMB) and relatively small message size, and send the76 bytes directly via the fast-path to NetBios of the server. NetBioswill give the data to SMB, which processes the Read request and fetchesthe 64 KB of data into server data buffers. SMB then calls NetBios tosend the data, and NetBios outputs the data for the client. In aconventional host, NetBios would call TCP output and pass 64 KB to TCP,which would divide the data into 1460 byte segments and output eachsegment via IP and eventually MAC (slow-path 231). In the present case,the 64 KB data goes to the ATCP driver along with an indicationregarding the client-server SMB connection, which indicates a CCB heldby the INIC. The INIC 200 then proceeds to DMA 1460 byte segments fromthe host buffers, add the appropriate headers for TCP, IP and MAC at onetime, and send the completed packets on the network 210 (fast-path 237).The INIC 200 will repeat this until the whole 64 KB transfer has beensent. Usually after receiving acknowledgement from the client that the64 KB has been received, the INIC will then send the remaining 36 KBalso by the fast-path 237.

[0083] With INIC 150 operating on the client 190 when this replyarrives, the INIC 150 recognizes from the first frame received that thisconnection is receiving fast-path 159 processing (TCP/IP, NetBios,matching a CCB), and the ATCP may use this first frame to acquire bufferspace for the message. This latter case is done by passing the first 128bytes of the NetBios portion of the frame via the ATCP fast-pathdirectly to the host NetBios; that will give NetBios/SMB all of theframe's headers. NetBios/SMB will analyze these headers, realize bymatching with a request ID that this is a reply to the original RawReadconnection, and give the ATCP a 64 K list of buffers into which to placethe data. At this stage only one frame has arrived, although more mayarrive while this processing is occurring. As soon as the client bufferlist is given to the ATCP, it passes that transfer information to theINIC 150, and the INIC 150 starts DMAing any frame data that hasaccumulated into those buffers.

[0084]FIG. 13 provides a simplified diagram of the INIC 200, whichcombines the functions of a network interface controller and a protocolprocessor in a single ASIC chip 400. The INIC 200 in this embodimentoffers a full-duplex, four channel, 10/100-Megabit per second (Mbps)intelligent network interface controller that is designed for high speedprotocol processing for server applications. Although designedspecifically for server applications, the INIC 200 can be connected topersonal computers, workstations, routers or other hosts anywhere thatTCP/IP, TTCP/IP or SPX/IPX protocols are being utilized.

[0085] The INIC 200 is connected with four network lines 210, 240, 242and 244, which may transport data along a number of different conduits,such as twisted pair, coaxial cable or optical fiber, each of theconnections providing a media independent interface (MI) viacommercially available physical layer chips, such as model 80220/80221Ethernet Media Interface Adapter from SEEQ Technology Incorporated,47200 Bayside Parkway, Fremont, Calif. 94538. The lines preferably are802.3 compliant and in connection with the INIC constitute four completeEthernet nodes, the INIC supporting 10Base-T, 10Base-T2, 100Base-TX,100Base-FX and 100Base-T4 as well as future interface standards.Physical layer identification and initialization is accomplished throughhost driver initialization routines. The connection between the networklines 210, 240, 242 and 244 and the INIC 200 is controlled by MAC unitsMAC-A 402, MAC-B 404, MAC-C 406 and MAC-D 408 which contain logiccircuits for performing the basic functions of the MAC sublayer,essentially controlling when the INIC accesses the network lines 210,240, 242 and 244. The MAC units 402-408 may act in promiscuous,multicast or unicast modes, allowing the INIC to function as a networkmonitor, receive broadcast and multicast packets and implement multipleMAC addresses for each node. The MAC units 402-408 also providestatistical information that can be used for simple network managementprotocol (SNMP).

[0086] The MAC units 402, 404, 406 and 408 are each connected to atransmit and receive sequencer, XMT & RCV-A 418, XMT & RCV-B 420, XMT &RCV-C 422 and XMT & RCV-D 424, by wires 410, 412, 414 and 416,respectively. Each of the transmit and receive sequencers can performseveral protocol processing steps on the fly as message frames passthrough that sequencer. In combination with the MAC units, the transmitand receive sequencers 418-422 can compile the packet status for thedata link, network, transport, session and, if appropriate, presentationand application layer protocols in hardware, greatly reducing the timefor such protocol processing compared to conventional sequentialsoftware engines. The transmit and receive sequencers 410-414 areconnected, by lines 426, 428, 430 and 432 to an SRAM and DMA controller444, which includes DMA controllers 438 and SRAM controller 442. Staticrandom access memory (SRAM) buffers 440 are coupled with SRAM controller442 by line 441. The SRAM and DMA controllers 444 interact across line446 with external memory control 450 to send and receive frames viaexternal memory bus 455 to and from dynamic random access memory (DRAM)buffers 460, which is located adjacent to the IC chip 400. The DRAMbuffers 460 may be configured as 4 MB, 8 MB, 16 MB or 32 MB, and mayoptionally be disposed on the chip. The SRAM and DMA controllers 444 areconnected via line 464 to a PCI Bus Interface Unit (BIU) 468, whichmanages the interface between the INIC 200 and the PCI interface bus257. The 64-bit, multiplexed BIU 468 provides a direct interface to thePCI bus 257 for both slave and master functions. The INIC 200 is capableof operating in either a 64-bit or 32-bit PCI environment, whilesupporting 64-bit addressing in either configuration.

[0087] A microprocessor 470 is connected by line 472 to the SRAM and DMAcontrollers 444, and connected via line 475 to the PCI BIU 468.Microprocessor 470 instructions and register files reside in an on chipcontrol store 480, which includes a writable on-chip control store (WCS)of SRAM and a read only memory (ROM), and is connected to themicroprocessor by line 477. The microprocessor 470 offers a programmablestate machine which is capable of processing incoming frames, processinghost commands, directing network traffic and directing PCI bus traffic.Three processors are implemented using shared hardware in a three levelpipelined architecture that launches and completes a single instructionfor every clock cycle. A receive processor 482 is primarily used forreceiving communications while a transmit processor 484 is primarilyused for transmitting communications in order to facilitate full duplexcommunication, while a utility processor 486 offers various functionsincluding overseeing and controlling PCI register access.

[0088] The instructions for the three processors 482, 484 and 486 residein the on-chip control-store 480. Thus the functions of the threeprocessors can be easily redefined, so that the microprocessor 470 canadapted for a given environment. For instance, the amount of processingrequired for receive functions may outweigh that required for eithertransmit or utility functions. In this situation, some receive functionsmay be performed by the transmit processor 484 and/or the utilityprocessor 486. Alternatively, an additional level of pipelining can becreated to yield four or more virtual processors instead of three, withthe additional level devoted to receive functions.

[0089] The INIC 200 in this embodiment can support up to 256 CCBs whichare maintained in a table in the DRAM 460. There is also, however, a CCBindex in hash order in the SRAM 440 to save sequential searching. Once ahash has been generated, the CCB is cached in SRAM, with up to sixteencached CCBs in SRAM in this example. Allocation of the sixteen CCBscached in SRAM is handled by a least recently used register, describedbelow. These cache locations are shared between the transmit 484 andreceive 486 processors so that the processor with the heavier load isable to use more cache buffers. There are also eight header buffers andeight command buffers to be shared between the sequencers. A givenheader or command buffer is not statically linked to a specific CCBbuffer, as the link is dynamic on a per-frame basis.

[0090]FIG. 14 shows an overview of the pipelined microprocessor 470, inwhich instructions for the receive, transmit and utility processors areexecuted in three alternating phases according to Clock increments I, IIand III, the phases corresponding to each of the pipeline stages. Eachphase is responsible for different functions, and each of the threeprocessors occupies a different phase during each Clock increment. Eachprocessor usually operates upon a different instruction stream from thecontrol store 480, and each carries its own program counter and statusthrough each of the phases.

[0091] In general, a first instruction phase 500 of the pipelinedmicroprocessors completes an instruction and stores the result in adestination operand, fetches the next instruction, and stores that nextinstruction in an instruction register. A first register set 490provides a number of registers including the instruction register, and aset of controls 492 for first register set provides the controls forstorage to the first register set 490. Some items pass through the firstphase without modification by the controls 492, and instead are simplycopied into the first register set 490 or a RAM file register 533. Asecond instruction phase 560 has an instruction decoder and operandmultiplexer 498 that generally decodes the instruction that was storedin the instruction register of the first register set 490 and gathersany operands which have been generated, which are then stored in adecode register of a second register set 496. The first register set490, second register set 496 and a third register set 501, which isemployed in a third instruction phase 600, include many of the sameregisters, as will be seen in the more detailed views of FIGS. 15A-C.The instruction decoder and operand multiplexer 498 can read from twoaddress and data ports of the RAM file register 533, which operates inboth the first phase 500 and second phase 560. A third phase 600 of theprocessor 470 has an arithmetic logic unit (ALU) 602 which generallyperforms any ALU operations on the operands from the second registerset, storing the results in a results register included in the thirdregister set 501. A stack exchange 608 can reorder register stacks, anda queue manager 503 can arrange queues for the processor 470, theresults of which are stored in the third register set. The instructionscontinue with the first phase then following the third phase, asdepicted by a circular pipeline 505. Note that various functions havebeen distributed across the three phases of the instruction execution inorder to minimize the combinatorial delays within any given phase. Witha frequency in this embodiment of 66 MHz, each Clock increment takes 15nanoseconds to complete, for a total of 45 nanoseconds to complete oneinstruction for each of the three processors. The rotating instructionphases are depicted in more detail in FIGS. 15A-C, in which each phaseis shown in a different figure.

[0092] More particularly, FIG. 15A shows some specific hardwarefunctions of the first phase 500, which generally includes the firstregister set 490 and related controls 492. The controls for the firstregister set 492 includes an SRAM control 502, which is a logicalcontrol for loading address and write data into SRAM address and dataregisters 520. Thus the output of the ALU 602 from the third phase 600may be placed by SRAM control 502 into an address register or dataregister of SRAM address and data registers 520. A load control 504similarly provides controls for writing a context for a file to filecontext register 522, and another load control 506 provides controls forstoring a variety of miscellaneous data to flip-flop registers 525. ALUcondition codes, such as whether a carried bit is set, get clocked intoALU condition codes register 528 without an operation performed in thefirst phase 500. Flag decodes 508 can perform various functions, such assetting locks, that get stored in flag registers 530.

[0093] The RAM file register 533 has a single write port for addressesand data and two read ports for addresses and data, so that more thanone register can be read from at one time. As noted above, the RAM fileregister 533 essentially straddles the first and second phases, as it iswritten in the first phase 500 and read from in the second phase 560. Acontrol store instruction 510 allows the reprogramming of the processorsdue to new data in from the control store 480, not shown in this figure,the instructions stored in an instruction register 535. The address forthis is generated in a fetch control register 511, which determineswhich address to fetch, the address stored in fetch address register538. Load control 515 provides instructions for a program counter 540,which operates much like the fetch address for the control store. Alast-in first-out stack 544 of three registers is copied to the firstregister set without undergoing other operations in this phase. Finally,a load control 517 for a debug address 548 is optionally included, whichallows correction of errors that may occur.

[0094]FIG. 15B depicts the second microprocessor phase 560, whichincludes reading addresses and data out of the RAM file register 533. Ascratch SRAM 565 is written from SRAM address and data register 520 ofthe first register set, which includes a register that passes throughthe first two phases to be incremented in the third. The scratch SRAM565 is read by the instruction decoder and operand multiplexer 498, asare most of the registers from the first register set, with theexception of the stack 544, debug address 548 and SRAM address and dataregister mentioned above. The instruction decoder and operandmultiplexer 498 looks at the various registers of set 490 and SRAM 565,decodes the instructions and gathers the operands for operation in thenext phase, in particular determining the operands to provide to the ALU602 below. The outcome of the instruction decoder and operandmultiplexer 498 is stored to a number of registers in the secondregister set 496, including ALU operands 579 and 582, ALU condition coderegister 580, and a queue channel and command 587 register, which inthis embodiment can control thirty-two queues. Several of the registersin set 496 are loaded fairly directly from the instruction register 535above without substantial decoding by the decoder 498, including aprogram control 590, a literal field 589, a test select 584 and a flagselect 585. Other registers such as the file context 522 of the firstphase 500 are always stored in a file context 577 of the second phase560, but may also be treated as an operand that is gathered by themultiplexer 572. The stack registers 544 are simply copied in stackregister 594. The program counter 540 is incremented 568 in this phaseand stored in register 592. Also incremented 570 is the optional debugaddress 548, and a load control 575 may be fed from the pipeline 505 atthis point in order to allow error control in each phase, the resultstored in debug address 598.

[0095]FIG. 15C depicts the third microprocessor phase 600, whichincludes ALU and queue operations. The ALU 602 includes an adder,priority encoders and other standard logic functions. Results of the ALUare stored in registers ALU output 618, ALU condition codes 620 anddestination operand results 622. A file context register 616, flagselect register 626 and literal field register 630 are simply copiedfrom the previous phase 560. A test multiplexer 604 is provided todetermine whether a conditional jump results in a jump, with the resultsstored in a test results register 624. The test multiplexer 604 mayinstead be performed in the first phase 500 along with similar decisionssuch as fetch control 511. A stack exchange 608 shifts a stack up ordown by fetching a program counter from stack 594 or putting a programcounter onto that stack, results of which are stored in program control634, program counter 638 and stack 640 registers. The SRAM address mayoptionally be incremented in this phase 600. Another load control 610for another debug address 642 may be forced from the pipeline 505 atthis point in order to allow error control in this phase also. A QRAM &QALU 606, shown together in this figure, read from the queue channel andcommand register 587, store in SRAM and rearrange queues, adding orremoving data and pointers as needed to manage the queues of data,sending results to the test multiplexer 604 and a queue flags and queueaddress register 628. Thus the QRAM & QALU 606 assume the duties ofmanaging queues for the three processors, a task conventionallyperformed sequentially by software on a CPU, the queue manager 606instead providing accelerated and substantially parallel hardwarequeuing.

[0096]FIG. 16 depicts two of the thirty-two hardware queues that aremanaged by the queue manager 606, with each of the queues having an SRAMhead, an SRAM tail and the ability to queue information in a DRAM bodyas well, allowing expansion and individual configuration of each queue.Thus FIFO 700 has SRAM storage units, 705, 707, 709 and 711, eachcontaining eight bytes for a total of thirty-two bytes, although thenumber and capacity of these units may vary in other embodiments.Similarly, FIFO 702 has SRAM storage units 713, 715, 717 and 719. SRAMunits 705 and 707 are the head of FIFO 700 and units 709 and 711 are thetail of that FIFO, while units 713 and 715 are the head of FIFO 702 andunits 717 and 719 are the tail of that FIFO. Information for FIFO 700may be written into head units 705 or 707, as shown by arrow 722, andread from tail units 711 or 709, as shown by arrow 725. A particularentry, however, may be both written to and read from head units 705 or707, or may be both written to and read from tail units 709 or 711,minimizing data movement and latency. Similarly, information for FIFO702 is typically written into head units 713 or 715, as shown by arrow733, and read from tail units 717 or 719, as shown by arrow 739, but mayinstead be read from the same head or tail unit to which it was written.

[0097] The SRAM FIFOS 700 and 702 are both connected to DRAM 460, whichallows virtually unlimited expansion of those FIFOS to handle situationsin which the SRAM head and tail are full. For example a first of thethirty-two queues, labeled Q-zero, may queue an entry in DRAM 460, asshown by arrow 727, by DMA units acting under direction of the queuemanager, instead of being queued in the head or tail of FIFO 700.Entries stored in DRAM 460 return to SRAM unit 709, as shown by arrow730, extending the length and fall-through time of that FIFO. Diversionfrom SRAM to DRAM is typically reserved for when the SRAM is full, sinceDRAM is slower and DMA movement causes additional latency. Thus Q-zeromay comprise the entries stored by queue manager 606 in both the FIFO700 and the DRAM 460. Likewise, information bound for FIFO 702, whichmay correspond to Q-twenty-seven, for example, can be moved by DMA intoDRAM 460, as shown by arrow 735. The capacity for queuing incost-effective albeit slower DRAM 460 is user-definable duringinitialization, allowing the queues to change in size as desired.Information queued in DRAM 460 is returned to SRAM unit 717, as shown byarrow 737.

[0098] Status for each of the thirty-two hardware queues is convenientlymaintained in and accessed from a set 740 of four, thirty-two bitregisters, as shown in FIG. 17, in which a specific bit in each registercorresponds to a specific queue. The registers are labeled Q-Out_Ready745, Q-In_Ready 750, Q-Empty 755 and Q-Full 760. If a particular bit isset in the Q-Out₁₃ Ready register 750, the queue corresponding to thatbit contains information that is ready to be read, while the setting ofthe same bit in the Q-In_Ready 752 register means that the queue isready to be written. Similarly, a positive setting of a specific bit inthe Q-Empty register 755 means that the queue corresponding to that bitis empty, while a positive setting of a particular bit in the Q-Fullregister 760 means that the queue corresponding to that bit is full.Thus Q-Out_Ready 745 contains bits zero 746 through thirty-one 748,including bits twenty-seven 752, twenty-eight 754, twenty-nine 756 andthirty 758. Q-In_Ready 750 contains bits zero 762 through thirty-one764, including bits twenty-seven 766, twenty-eight 768, twenty-nine 770and thirty 772. Q-Empty 755 contains bits zero 774 through thirty-one776, including bits twenty-seven 778, twenty-eight 780, twenty-nine 782arid thirty 784, and Q-full 760 contains bits zero 786 throughthirty-one 788, including bits twenty-seven 790, twenty-eight 792,twenty-nine 794 and thirty 796.

[0099] Q-zero, corresponding to FIFO 700, is a free buffer queue, whichholds a list of addresses for all available buffers. This queue isaddressed when the microprocessor or other devices need a free bufferaddress, and so commonly includes appreciable DRAM 460. Thus a deviceneeding a free buffer address would check with Q-zero to obtain thataddress. Q-twenty-seven, corresponding to FIFO 702, is a receive bufferdescriptor queue. After processing a received frame by the receivesequencer the sequencer looks to store a descriptor for the frame inQ-twenty-seven. If a location for such a descriptor is immediatelyavailable in SRAM, bit twenty-seven 766 of Q-In_Ready 750 will be set.If not, the sequencer must wait for the queue manager to initiate a DMAmove from SRAM to DRAM, thereby freeing space to store the receivedescriptor.

[0100] Operation of the queue manager, which manages movement of queueentries between SRAM and the processor, the transmit and receivesequencers, and also between SRAM and DRAM, is shown in more detail inFIG. 18. Requests which utilize the queues include Processor Request802, Transmit Sequencer Request 804, and Receive Sequencer Request 806.Other requests for the queues are DRAM to SRAM Request 808 and SRAM toDRAM Request 810, which operate on behalf of the queue manager in movingdata back and forth between the DRAM and the SRAM head or tail of thequeues. Determining which of these various requests will get to use thequeue manager in the next cycle is handled by priority logic Arbiter815. To enable high frequency operation the queue manager is pipelined,with Register A 818 and Register B 820 providing temporary storage,while Status Register 822 maintains status until the next update. Thequeue manager reserves even cycles for DMA, receive and transmitsequencer requests and odd cycles for processor requests. Dual portedQRAM 825 stores variables regarding each of the queues, the variablesfor each queue including a Head Write Pointer, Head Read Pointer, TailWrite Pointer and Tail Read Pointer corresponding to the queue's SRAMcondition, and a Body Write Pointer and Body Read Pointer correspondingto the queue's DRAM condition and the queue's size.

[0101] After Arbiter 815 has selected the next operation to beperformed, the variables of QRAM 825 are fetched and modified accordingto the selected operation by a QALU 828, and an SRAM Read Request 830 oran SRAM Write Request 840 may be generated. The variables are updatedand the updated status is stored in Status Register 822 as well as QRAM825. The status is also fed to Arbiter 815 to signal that the operationpreviously requested has been fulfilled, inhibiting duplication ofrequests. The Status Register 822 updates the four queue registersQ-Out_Ready 745, Q-In_Ready 750, Q-Empty 755 and Q-Full 760 to reflectthe new status of the queue that was accessed. Similarly updated areSRAM Addresses 833, Body Write Request 835 and Body Read Requests 838,which are accessed via DMA to and from SRAM head and tails for thatqueue. Alternatively, various processes may wish to write to a queue, asshown by Q Write Data 844, which are selected by multiplexor 846, andpipelined to SRAM Write Request 840. The SRAM controller services theread and write requests by writing the tail or reading the head of theaccessed queue and returning an acknowledge. In this manner the variousqueues are utilized and their status updated.

[0102] FIGS. 19A-C show a least-recently-used register 900 that isemployed for choosing which contexts or CCBs to maintain in INIC cachememory. The INIC in this embodiment can cache up to sixteen CCBs in SRAMat a given time, and so when a new CCB is cached an old one must oftenbe discarded, the discarded CCB usually chosen according to thisregister 900 to be the CCB that has been used least recently. In thisembodiment, a hash table for up to two hundred fifty-six CCBs is alsomaintained in SRAM, while up to two hundred fifty-six full CCBs are heldin DRAM. The least-recently-used register 900 contains sixteen four-bitblocks labeled R0-R15, each of which corresponds to an SRAM cache unit.Upon initialization, the blocks are numbered 0-15, with number 0arbitrarily stored in the block representing the least recently used(LRU) cache unit and number 15 stored in the block representing the mostrecently used (MRU) cache unit. FIG. 19A shows the register 900 at anarbitrary time when the LRU block R0 holds the number 9 and the MRUblock R15 holds the number 6.

[0103] When a different CCB than is currently being held in SRAM is tobe cached, the LRU block R0 is read, which in FIG. 19A holds the number9, and the new CCB is stored in the SRAM cache unit corresponding tonumber 9. Since the new CCB corresponding to number 9 is now the mostrecently used CCB, the number 9 is stored in the MRU block, as shown inFIG. 19B. The other numbers are all shifted one register block to theleft, leaving the number 1 in the LRU block. The CCB that had previouslybeen cached in the SRAM unit corresponding to number 9 has been moved toslower but more cost-effective DRAM.

[0104]FIG. 19C shows the result when the next CCB used had already beencached in SRAM. In this example, the CCB was cached in an SRAM unitcorresponding to number 10, and so after employment of that CCB, number10 is stored in the MRU block. Only those numbers which had previouslybeen more recently used than number 10 (register blocks R9-R15) areshifted to the left, leaving the number 1 in the LRU block. In thismanner the INIC maintains the most active CCBs in SRAM cache.

[0105] In some cases a CCB being used is one that is not desirable tohold in the limited cache memory. For example, it is preferable not tocache a CCB for a context that is known to be closing, so that othercached CCBs can remain in SRAM longer. In this case, the numberrepresenting the cache unit holding the decacheable CCB is stored in theLRU block R0 rather than the MRU block R15, so that the decacheable CCBwill be replaced immediately upon employment of a new CCB that is cachedin the SRAM unit corresponding to the number held in the LRU block R0.FIG. 19D shows the case for which number 8 (which had been in block R9in FIG. 19C) corresponds to a CCB that will be used and then closed. Inthis case number 8 has been removed from block R9 and stored in the LRUblock R0. All the numbers that had previously been stored to the left ofblock R9 (R1-R8) are then shifted one block to the right.

[0106]FIG. 20 shows some of the logical units employed to operate theleast-recently-used register 900. An array of sixteen, three or fourinput multiplexors 910, of which only multiplexors MUX0, MUX7, MUX8,MUX9 and MUX15 are shown for clarity, have outputs fed into thecorresponding sixteen blocks of least-recently-used register 900. Forexample, the output of MUX0 is stored in block R0, the output of MUX7 isstored in block R7, etc. The value of each of the register blocks isconnected to an input for its corresponding multiplexor and also intoinputs for both adjacent multiplexors, for use in shifting the blocknumbers. For instance, the number stored in R8 is fed into inputs forMUX7, MUX8 and MUX9. MUX0 and MUX15 each have only one adjacent block,and the extra input for those multiplexors is used for the selection ofLRU and MRU blocks, respectively. MUX15 is shown as a four-inputmultiplexor, with input 915 providing the number stored on R0.

[0107] An array of sixteen comparators 920 each receives the valuestored in the corresponding block of the least-recently-used register900. Each comparator also receives a signal from processor 470 alongline 935 so that the register block having a number matching that sentby processor 470 outputs true to logic circuits 930 while the otherfifteen comparators output false. Logic circuits 930 control a pair ofselect lines leading to each of the multiplexors, for selecting inputsto the multiplexors and therefore controlling shifting of the registerblock numbers. Thus select lines 939 control MUX0, select lines 944control MUX7, select lines 949 control MUX8, select lines 954 controlMUX9 and select lines 959 control MUX15.

[0108] When a CCB is to be used, processor 470 checks to see whether theCCB matches a CCB currently held in one of the sixteen cache units. If amatch is found, the processor sends a signal along line 935 with theblock number corresponding to that cache unit, for example number 12.Comparators 920 compare the signal from that line 935 with the blocknumbers and comparator C8 provides a true output for the block R8 thatmatches the signal, while all the other comparators output false. Logiccircuits 930, under control from the processor 470, use select lines 959to choose the input from line 935 for MUX15, storing the number 12 inthe MRU block R15. Logic circuits 930 also send signals along the pairsof select lines for MUX8 and higher multiplexors, aside from MUX15, toshift their output one block to the left, by selecting as inputs to eachmultiplexor MUX8 and higher the value that had been stored in registerblocks one block to the right (R9-R15). The outputs of multiplexors thatare to the left of MUX8 are selected to be constant.

[0109] If processor 470 does not find a match for the CCB among thesixteen cache units, on the other hand, the processor reads from LRUblock R0 along line 966 to identify the cache corresponding to the LRUblock, and writes the data stored in that cache to DRAM. The number thatwas stored in R0, in this case number 3, is chosen by)select lines 959as input 915 to MUX15 for storage in MRU block R15. The other fifteenmultiplexors output to their respective register blocks the numbers thathad been stored each register block immediately to the right.

[0110] For the situation in which the processor wishes to remove a CCBfrom the cache after use, the LRU block R0 rather than the MRU block R15is selected for placement of the number corresponding to the cache unitholding that CCB. The number corresponding to the CCB to be placed inthe LRU block R0 for removal from SRAM (for example number 1, held inblock R9) is sent by processor 470 along line 935, which is matched bycomparator C9. The processor instructs logic circuits 930 to input thenumber 1 to R0, by selecting with lines 939 input 935 to MUX0. Selectlines 954 to MUX9 choose as input the number held in register block R8,so that the number from R8 is stored in R9. The numbers held by theother register blocks between R0 and R9 are similarly shifted to theright, whereas the numbers in register blocks to the right of R9 areleft constant. This frees scarce cache memory from maintaining closedCCBs for many cycles while their identifying numbers move throughregister blocks from the MRU to the LRU blocks.

[0111]FIG. 21 is another diagram of Intelligent Network Interface Card(INIC) 200 of FIG. 13. INIC card 200 includes a Physical Layer Interface(PHY) chip 2100, ASIC chip 400 and Dynamic Random Access Memory (DRAM)460. PHY chip 2100 couples INIC card 200 to network line 210 via anetwork connector 2101. INIC card 200 is coupled to the CPU of the host(for example, CPU 28 of host 20 of FIG. 1) via card edge connector 2107and PCI bus 257. ASIC chip 400 includes a Media Access Control (MAC)unit 402, a sequencers block 2103, SRAM control 442, SRAM 440, DRAMcontrol 450, a queue manager 2103, a processor 470, and a PCI businterface unit 468. Structure and operation of queue manager 2103 isdescribed above in connection with FIG. 18 and in U.S. patentapplication Ser. No. 09/416,925, entitled “Queue System ForMicroprocessors”, attorney docket no. ALA-005, filed Oct. 13, 1999, byDaryl D. Starr and Clive M. Philbrick (the subject matter of which isincorporated herein by reference). Sequencers block 2102 includes atransmit sequencer 2104, a receive sequencer 2105, and configurationregisters 2106. A MAC destination address is stored in configurationregister 2106. Part of the program code executed by processor 470 iscontained in ROM (not shown) and part is located in a writeable controlstore SRAM (not shown). The program is downloaded into the writeablecontrol store SRAM at initialization from the host 20.

[0112]FIG. 22 is a more detailed diagram of receive sequencer 2105.Receive sequencer 2105 includes a data synchronization buffer 2200, apacket synchronization sequencer 2201, a data assembly register 2202, aprotocol analyzer 2203, a packet processing sequencer 2204, a queuemanager interface 2205, and a Direct Memory Access (DMA) control block2206. The packet synchronization sequencer 2201 and data synchronizationbuffer 2200 utilize a network-synchronized clock of MAC 402, whereas theremainder of the receive sequencer 2105 utilizes a fixed-frequencyclock. Dashed line 2221 indicates the clock domain boundary.

[0113] CD Appendix A contains a complete hardware description (verilogcode) of an embodiment of receive sequencer 2105. Signals in the verilogcode are named to designate their functions. Individual sections of theverilog code are identified and labeled with comment lines. Each ofthese sections describes hardware in a block of the receive sequencer2105 as set forth below in Table 1. TABLE 1 SECTION OF VERILOG CODEBLOCK OF FIG. 22 Synchronization Interface 2201 Sync-Buffer Read-PtrSynchronizers 2201 Packet-Synchronization Sequencer 2201 DataSynchronization Buffer 2201 and 2200 Synchronized Status forLink-Destination-Address 2201 Synchronized Status-Vector 2201Synchronization Interface 2204 Receive Packet Control and Status 2204Buffer-Descriptor 2201 Ending Packet Status 2201 AssyReg shift-in. Mac-> AssyReg. 2202 and 2204 Fifo shift-in. AssyReg -> Sram Fifo 2206 FifoShiftOut Burst. SramFifo -> DramBuffer 2206 Fly-By Protocol Analyzer;Frame, 2203 Network and Transport Layers Link Pointer 2203 Mac addressdetection 2203 Magic pattern detection 2203 Link layer and network layerdetection 2203 Network counter 2203 Control Packet analysis 2203 Networkheader analysis 2203 Transport layer counter 2203 Transport headeranalysis 2203 Pseudo-header stuff 2203 Free-Descriptor Fetch 2205Receive-Descriptor Store 2205 Receive-Vector Store 2205 Queue-managerinterface-mux 2205 Pause Clock Generator 2201 Pause Timer 2204

[0114] Operation of receive sequencer 2105 of FIGS. 21 and 22 is nowdescribed in connection with the receipt onto INIC card 200 of a TCP/IPpacket from network line 210. At initialization time, processor 470partitions DRAM 460 into buffers. Receive sequencer 2105 uses thebuffers in DRAM 460 to store incoming network packet data as well asstatus information for the packet. Processor 470 creates a 32-bit bufferdescriptor for each buffer. A buffer descriptor indicates the size andlocation in DRAM of its associated buffer. Processor 470 places thesebuffer descriptors on a “free-buffer queue” 2108 by writing thedescriptors to the queue manager 2103. Queue manager 2103 maintainsmultiple queues including the “free-buffer queue” 2108. In thisimplementation, the heads and tails of the various queues are located inSRAM 440, whereas the middle portion of the queues are located in DRAM460.

[0115] Lines 2229 comprise a request mechanism involving a request lineand address lines. Similarly, lines 2230 comprise a request mechanisminvolving a request line and address lines. Queue manager 2103 useslines 2229 and 2230 to issue requests to transfer queue information fromDRAM to SRAM or from SRAM to DRAM.

[0116] The queue manager interface 2205 of the receive sequencer alwaysattempts to maintain a free buffer descriptor 2207 for use by the packetprocessing sequencer 2204. Bit 2208 is a ready bit that indicates thatfree-buffer descriptor 2207 is available for use by the packetprocessing sequencer 2204. If queue manager interface 2205 does not havea free buffer descriptor (bit 2208 is not set), then queue managerinterface 2205 requests one from queue manager 2103 via request line2209. (Request line 2209 is actually a bus which communicates therequest, a queue ID, a read/write signal and data if the operation is awrite to the queue.)

[0117] In response, queue manager 2103 retrieves a free bufferdescriptor from the tail of the “free buffer queue” 2108 and then alertsthe queue manager interface 2205 via an acknowledge signal onacknowledge line 2210. When queue manager interface 2205 receives theacknowledge signal, the queue manager interface 2205 loads the freebuffer descriptor 2207 and sets the ready bit 2208. Because the freebuffer descriptor was in the tail of the free buffer queue in SRAM 440,the queue manager interface 2205 actually receives the free bufferdescriptor 2207 from the read data bus 2228 of the SRAM control block442. Packet processing sequencer 2204 requests a free buffer descriptor2207 via request line 2211. When the queue manager interface 2205retrieves the free buffer descriptor 2207 and the free buffer descriptor2207 is available for use by the packet processing sequencer, the queuemanager interface 2205 informs the packet processing sequencer 2204 viagrant line 2212. By this process, a free buffer descriptor is madeavailable for use by the packet processing sequencer 2204 and thereceive sequencer 2105 is ready to processes an incoming packet.

[0118] Next, a TCP/IP packet is received from the network line 210 vianetwork connector 2101 and Physical Layer Interface (PHY) 2100. PHY 2100supplies the packet to MAC 402 via a Media Independent Interface (MII)parallel bus 2109. MAC 402 begins processing the packet and asserts a“start of packet” signal on line 2213 indicating that the beginning of apacket is being received. When a byte of data is received in the MAC andis available at the MAC outputs 2215, MAC 402 asserts a “data valid”signal on line 2214. Upon receiving the “data valid” signal, the packetsynchronization sequencer 2201 instructs the data synchronization buffer2200 via load signal line 2222 to load the received byte from data lines2215. Data synchronization buffer 2200 is four bytes deep. The packetsynchronization sequencer 2201 then increments a data synchronizationbuffer write pointer. This data synchronization buffer write pointer ismade available to the packet processing sequencer 2204 via lines 2216.Consecutive bytes of data from data lines 2215 are clocked into the datasynchronization buffer 2200 in this way.

[0119] A data synchronization buffer read pointer available on lines2219 is maintained by the packet processing sequencer 2204. The packetprocessing sequencer 2204 determines that data is available in datasynchronization buffer 2200 by comparing the data synchronization bufferwrite pointer on lines 2216 with the data synchronization buffer readpointer on lines 2219.

[0120] Data assembly register 2202 contains a sixteen-byte long shiftregister 2217. This register 2217 is loaded serially a single byte at atime and is unloaded in parallel. When data is loaded into register2217, a write pointer is incremented. This write pointer is madeavailable to the packet processing sequencer 2204 via lines 2218.Similarly, when data is unloaded from register 2217, a read pointermaintained by packet processing sequencer 2204 is incremented. This readpointer is available to the data assembly register 2202 via lines 2220.The packet processing sequencer 2204 can therefore determine whetherroom is available in register 2217 by comparing the write pointer onlines 2218 to the read pointer on lines 2220.

[0121] If the packet processing sequencer 2204 determines that room isavailable in register 2217, then packet processing sequencer 2204instructs data assembly register 2202 to load a byte of data from datasynchronization buffer 2200. The data assembly register 2202 incrementsthe data assembly register write pointer on lines 2218 and the packetprocessing sequencer 2204 increments the data synchronization bufferread pointer on lines 2219. Data shifted into register 2217 is examinedat the register outputs by protocol analyzer 2203 which verifieschecksums, and generates “status” information 2223.

[0122] DMA control block 2206 is responsible for moving information fromregister 2217 to buffer 2114 via a sixty-four byte receive FIFO 2110.DMA control block 2206 implements receive FIFO 2110 as two thirty-twobyte ping-pong buffers using sixty-four bytes of SRAM 440. DMA controlblock 2206 implements the receive FIFO using a write-pointer and aread-pointer. When data to be transferred is available in register 2217and space is available in FIFO 2110, DMA control block 2206 asserts anSRAM write request to SRAM controller 442 via lines 2225. SRAMcontroller 442 in turn moves data from register 2217 to FIFO 2110 andasserts an acknowledge signal back to DMA control block 2206 via lines2225. DMA control block 2206 then increments the receive FIFO writepointer and causes the data assembly register read pointer to beincremented.

[0123] When thirty-two bytes of data has been deposited into receiveFIFO 2110, DMA control block 2206 presents a DRAM write request to DRAMcontroller 450 via lines 2226. This write request consists of the freebuffer descriptor 2207 ORed with a “buffer load count” for the DRAMrequest address, and the receive FIFO read pointer for the SRAM readaddress. Using the receive FIFO read pointer, the DRAM controller 450asserts a read request to SRAM controller 442. SRAM controller 442responds to DRAM controller 450 by returning the indicated data from thereceive FIFO 2110 in SRAM 440 and asserting an acknowledge signal. DRAMcontroller 450 stores the data in a DRAM write data register, stores aDRAM request address in a DRAM address register, and asserts anacknowledge to DMA control block 2206. The DMA control block 2206 thendecrements the receive FIFO read pointer. Then the DRAM controller 450moves the data from the DRAM write data register to buffer 2114. In thisway, as consecutive thirty-two byte chunks of data are stored in SRAM440, DRAM control block 2206 moves those thirty-two byte chunks of dataone at a time from SRAM 440 to buffer 2214 in DRAM 460. Transferringthirty-two byte chunks of data to the DRAM 460 in this fashion allowsdata to be written into the DRAM using the relatively efficient burstmode of the DRAM.

[0124] Packet data continues to flow from network line 210 to buffer2114 until all packet data has been received. MAC 402 then indicatesthat the incoming packet has completed by asserting an “end of frame”(i.e., end of packet) signal on line 2227 and by presenting final packetstatus (MAC packet status) to packet synchronization sequencer 2204. Thepacket processing sequencer 2204 then moves the status 2223 (also called“protocol analyzer status”) and the MAC packet status to register 2217for eventual transfer to buffer 2114. After all the data of the packethas been placed in buffer 2214, status 2223 and the MAC packet status istransferred to buffer 2214 so that it is stored prepended to theassociated data as shown in FIG. 22.

[0125] After all data and status has been transferred to buffer 2114,packet processing sequencer 2204 creates a summary 2224 (also called a“receive packet descriptor”) by concatenating the free buffer descriptor2207, the buffer load-count, the MAC ID, and a status bit (also calledan “attention bit”). If the attention bit is a one, then the packet isnot a “fast-path candidate”; whereas if the attention bit is a zero,then the packet is a “fast-path candidate”. The value of the attentionbit represents the result of a significant amount of processing thatprocessor 470 would otherwise have to do to determine whether the packetis a “fast-path candidate”. For example, the attention bit being a zeroindicates that the packet employs both TCP protocol and IP protocol. Bycarrying out this significant amount of processing in hardwarebeforehand and then encoding the result in the attention bit, subsequentdecision making by processor 470 as to whether the packet is an actual“fast-path packet” is accelerated. A complete logical description of theattention bit in verilog code is set forth in CD Appendix A in the linesfollowing the heading “Ending Packet Status”.

[0126] Packet processing sequencer 2204 then sets a ready bit (notshown) associated with summary 2224 and presents summary 2224 to queuemanager interface 2205. Queue manager interface 2205 then requests awrite to the head of a “summary queue” 2112 (also called the “receivedescriptor queue”). The queue manager 2103 receives the request, writesthe summary 2224 to the head of the summary queue 2212, and asserts anacknowledge signal back to queue manager interface via line 2210. Whenqueue manager interface 2205 receives the acknowledge, queue managerinterface 2205 informs packet processing sequencer 2204 that the summary2224 is in summary queue 2212 by clearing the ready bit associated withthe summary. Packet processing sequencer 2204 also generates additionalstatus information (also called a “vector”) for the packet byconcatenating the MAC packet status and the MAC ID. Packet processingsequencer 2204 sets a ready bit (not shown) associated with this vectorand presents this vector to the queue manager interface 2205. The queuemanager interface 2205 and the queue manager 2103 then cooperate towrite this vector to the head of a “vector queue” 2113 in similarfashion to the way summary 2224 was written to the head of summary queue2112 as described above. When the vector for the packet has been writtento vector queue 2113, queue manager interface 2205 resets the ready bitassociated with the vector.

[0127] Once summary 2224 (including a buffer descriptor that points tobuffer 2114) has been placed in summary queue 2112 and the packet datahas been placed in buffer 2144, processor 470 can retrieve summary 2224from summary queue 2112 and examine the “attention bit”.

[0128] If the attention bit from summary 2224 is a digital one, thenprocessor 470 determines that the packet is not a “fast-path candidate”and processor 470 need not examine the packet headers. Only the status2223 (first sixteen bytes) from buffer 2114 are DMA transferred to SRAMso processor 470 can examine it. If the status 2223 indicates that thepacket is a type of packet that is not to be transferred to the host(for example, a multicast frame that the host is not registered toreceive), then the packet is discarded (i.e., not passed to the host).If status 2223 does not indicate that the packet is the type of packetthat is not to be transferred to the host, then the entire packet(headers and data) is passed to a buffer on host 20 for “slow-path”transport and network layer processing by the protocol stack of host 20.

[0129] If, on the other hand, the attention bit is a zero, thenprocessor 470 determines that the packet is a “fast-path candidate”. Ifprocessor 470 determines that the packet is a “fast-path candidate”,then processor 470 uses the buffer descriptor from the summary to DMAtransfer the first approximately 96 bytes of information from buffer2114 from DRAM 460 into a portion of SRAM 440 so processor 470 canexamine it. This first approximately 96 bytes contains status 2223 aswell as the IP source address of the IP header, the IP destinationaddress of the IP header, the TCP source address of the TCP header, andthe TCP destination address of the TCP header. The IP source address ofthe IP header, the IP destination address of the IP header, the TCPsource address of the TCP header, and the TCP destination address of theTCP header together uniquely define a single connection context (TCB)with which the packet is associated. Processor 470 examines theseaddresses of the TCP and IP headers and determines the connectioncontext of the packet. Processor 470 then checks a list of connectioncontexts that are under the control of INIC card 200 and determineswhether the packet is associated with a connection context (TCB) underthe control of INIC card 200.

[0130] If the connection context is not in the list, then the “fast-pathcandidate” packet is determined not to be a “fast-path packet.” In sucha case, the entire packet (headers and data) is transferred to a bufferin host 20 for “slow-path” processing by the protocol stack of host 20.

[0131] If, on the other hand, the connection context is in the list,then software executed by processor 470 including software statemachines 2231 and 2232 checks for one of numerous exception conditionsand determines whether the packet is a “fast-path packet” or is not a“fast-path packet”. These exception conditions include: 1) IPfragmentation is detected; 2) an IP option is detected; 3) an unexpectedTCP flag (urgent bit set, reset bit set, SYN bit set or FIN bit set) isdetected; 4) the ACK field in the TCP header is before the TCP window,or the ACK field in the TCP header is after the TCP window, or the ACKfield in the TCP header shrinks the TCP window; 5) the ACK field in theTCP header is a duplicate ACK and the ACK field exceeds the duplicateACK count (the duplicate ACK count is a user settable value); and 6) thesequence number of the TCP header is out of order (packet is receivedout of sequence). If the software executed by processor 470 detects oneof these exception conditions, then processor 470 determines that the“fast-path candidate” is not a “fast-path packet.” In such a case, theconnection context for the packet is “flushed” (the connection contextis passed back to the host) so that the connection context is no longerpresent in the list of connection contexts under control of INIC card200. The entire packet (headers and data) is transferred to a buffer inhost 20 for “slow-path” transport layer and network layer processing bythe protocol stack of host 20.

[0132] If, on the other hand, processor 470 finds no such exceptioncondition, then the “fast-path candidate” packet is determined to be anactual “fast-path packet”. The receive state machine 2232 then processesof the packet through TCP. The data portion of the packet in buffer 2114is then transferred by another DMA controller (not shown in FIG. 21)from buffer 2114 to a host-allocated file cache in storage 35 of host20. In one embodiment, host 20 does no analysis of the TCP and IPheaders of a “fast-path packet”. All analysis of the TCP and IP headersof a “fast-path packet” is done on INIC card 20.

[0133]FIG. 23 is a diagram illustrating the transfer of data of“fast-path packets” (packets of a 64 k-byte session layer message 2300)from INIC 200 to host 20. The portion of the diagram to the left of thedashed line 2301 represents INIC 200, whereas the portion of the diagramto the right of the dashed line 2301 represents host 20. The 64 k-bytesession layer message 2300 includes approximately forty-five packets,four of which (2302, 2303, 2304 and 2305) are labeled on FIG. 23. Thefirst packet 2302 includes a portion 2306 containing transport andnetwork layer headers (for example, TCP and IP headers), a portion 2307containing a session layer header, and a portion 2308 containing data.In a first step, portion 2307, the first few bytes of data from portion2308, and the connection context identifier 2310 of the packet 2300 aretransferred from INIC 200 to a 256-byte buffer 2309 in host 20. In asecond step, host 20 examines this information and returns to INIC 200 adestination (for example, the location of a file cache 2311 in storage35) for the data. Host 20 also copies the first few bytes of the datafrom buffer 2309 to the beginning of a first part 2312 of file cache2311. In a third step, INIC 200 transfers the remainder of the data fromportion 2308 to host 20 such that the remainder of the data is stored inthe remainder of first part 2312 of file cache 2311. No network,transport, or session layer headers are stored in first part 2312 offile cache 2311. Next, the data portion 2313 of the second packet 2303is transferred to host 20 such that the data portion 2313 of the secondpacket 2303 is stored in a second part 2314 of file cache 2311. Thetransport layer and network layer header portion 2315 of second packet2303 is not transferred to host 20. There is no network, transport, orsession layer header stored in file cache 2311 between the data portionof first packet 2302 and the data portion of second packet 2303.Similarly, the data portion 2316 of the next packet 2304 of the sessionlayer message is transferred to file cache 2311 so that there is nonetwork, transport, or session layer headers between the data portion ofthe second packet 2303 and the data portion of the third packet 2304 infile cache 2311. In this way, only the data portions of the packets ofthe session layer message are placed in the file cache 2311. The datafrom the session layer message 2300 is present in file cache 2311 as ablock such that this block contains no network, transport, or sessionlayer headers.

[0134] In the case of a shorter, single-packet session layer message,portions 2307 and 2308 of the session layer message are transferred to256-byte buffer 2309 of host 20 along with the connection contextidentifier 2310 as in the case of the longer session layer messagedescribed above. In the case of a single-packet session layer message,however, the transfer is completed at this point. Host 20 does notreturn a destination to INIC 200 and INIC 200 does not transfersubsequent data to such a destination.

[0135] CD Appendix B includes a listing of software executed byprocessor 470 that determines whether a “fast-path candidate” packet isor is not a “fast-path packet”. An example of the instruction set ofprocessor 470 is found starting on page 79 of the Provisional U.S.Patent Application Serial No. 60/061,809, entitled “Intelligent NetworkInterface Card And System For Protocol Processing”, filed Oct. 14, 1997(the subject matter of this provisional application is incorporatedherein by reference).

[0136] CD Appendix C includes device driver software executable on host20 that interfaces the host 20 to INIC card 200. There is also ATCP codethat executes on host 20. This ATCP code includes: 1) a “free BSD” stack(available from the University of California, Berkeley) that has beenmodified slightly to make it run on the NT4 operating system (the “freeBSD” stack normally runs on a UNIX machine), and 2) code added to thefree BSD stack between the session layer above and the device driverbelow that enables the BSD stack to carry out “fast-path” processing inconjunction with INIC 200.

[0137] TRANSMIT FAST-PATH PROCESSING: The following is an overview ofone embodiment of a transmit fast-path flow once a command has beenposted (for additional information, see provisional application No.60/098,296, filed Aug. 27, 1998). The transmit request may be a segmentthat is less than the MSS, or it may be as much as a full 64 K sessionlayer packet. The former request will go out as one segment, the latteras a number of MSS-sized segments. The transmitting CCB must hold on tothe request until all data in it has been transmitted and ACKed.Appropriate pointers to do this are kept in the CCB. To create an outputTCP/IP segment, a large DRAM buffer is acquired from the Q_FREEL queue.Then data is DMAd from host memory into the DRAM buffer to create anMSS-sized segment. This DMA also checksums the data. The TCP/IP headeris created in SRAM and DMAd to the front of the payload data. It isquicker and simpler to keep a basic frame header (i.e., a templateheader) permanently in the CCB and DMA this directly from the SRAM CCBbuffer into the DRAM buffer each time. Thus the payload checksum isadjusted for the pseudo-header (i.e., the template header) and placedinto the TCP header prior to DMAing the header from SRAM. Then the DRAMbuffer is queued to the appropriate Q_UXMT transmit queue. The finalstep is to update various window fields etc in the CCB. Eventuallyeither the entire request will have been sent and ACKed, or aretransmission timer will expire in which case the context is flushed tothe host. In either case, the INIC will place a command response in theresponse queue containing the command buffer from the original transmitcommand and appropriate status.

[0138] The above discussion has dealt with how an actual transmitoccurs. However the real challenge in the transmit processor is todetermine whether it is appropriate to transmit at the time a transmitrequest arrives, and then to continue to transmit for as long as thetransport protocol permits. There are many reasons not to transmit: thereceiver's window size is less than or equal to zero, the persist timerhas expired, the amount to send is less than a full segment and an ACKis expected/outstanding, the receiver's window is not half-open, etc.Much of transmit processing will be in determining these conditions.

[0139] The fast-path is implemented as a finite state machine (FSM) thatcovers at least three layers of the protocol stack, i.e., IP, TCP, andSession. The following summarizes the steps involved in normal fast-pathtransmit command processing: 1) get control of the associated CCB(gotten from the command): this involves locking the CCB to stop otherprocessing (e.g. Receive) from altering it while this transmitprocessing is taking place. 2) Get the CCB into an SRAM CCB buffer.There are sixteen of these buffers in SRAM and they are not flushed toDRAM until the buffer space is needed by other CCBs. Acquisition andflushing of these CCB buffers is controlled by a hardware LRU mechanism.Thus getting into a buffer may involve flushing another CCB from itsSRAM buffer. 3) Process the send command (EX_SCMD) event against theCCB's FSM.

[0140] Each event and state intersection provides an action to beexecuted and a new state. The following is an example of the state/eventtransition, the action to be executed and the new state for the SENDcommand while in transmit state IDLE (SX_IDLE). The action from thisstate/event intersection is AX_NUCMD and the next state is XMIT COMMANDACTIVE (SX_XMIT). To summarize, a command to transmit data has beenreceived while transmit is currently idle. The action performs thefollowing steps: 1) Store details of the command into the CCB. 2) Checkthat it is okay to transmit now (e.g. send window is not zero). 3) Ifoutput is not possible, send the Check Output event to Q_EVENT1 queuefor the Transmit CCB's FSM and exit. 4) Get a DRAM 2 K-byte buffer fromthe Q-FREEL queue into which to move the payload data. 5) DMA payloaddata from the addresses in the scatter/gather lists in the command intoan offset in the DRAM buffer that leaves space for the frame header.These DMAs will provide the checksum of the payload data. 6)Concurrently with the above DMA, fill out variable details in the frameheader template in the CCB. Also get the IP and TCP header checksumswhile doing this. Note that base IP and TCP headers checksums are keptin the CCB, and these are simply updated for fields that vary per frame,viz. IP Id, IP length, IP checksum, TCP sequence and ACK numbers, TCPwindow size, TCP flags and TCP checksum. 7) When the payload iscomplete, DMA the frame header from the CCB to the front of the DRAMbuffer. 8) Queue the DRAM buffer (i.e., queue a buffer descriptor thatpoints to the DRAM buffer) to the appropriate Q_UXMT queue for theinterface for this CCB. 9) Determine if there is more payload in thecommand. If so, save the current command transfer address details in theCCB and send a CHECK OUTPUT event via the Q_EVENT1 queue to the TransmitCCB. If not, send the ALL COMMAND DATA SENT (EX_ACDS) event to theTransmit CCB. 10) Exit from Transmit FSM processing.

[0141] Code that implements an embodiment of the Transmit FSM (transmitsoftware state machine 2231 of FIG. 21) is found in CD Appendix B. Inone embodiment, fast-path transmit processing is controlled using writeonly transmit configuration register (XmtCfg). Register XmtCfg has thefollowing portions: 1) Bit 31 (name: Reset). Writing a one (1) willforce reset asserted to the transmit sequencer of the channel selectedby XcvSel. 2) Bit 30 (name: XmtEn). Writing a one (1) allows thetransmit sequencer to run. Writing a zero (0) causes the transmitsequencer to halt after completion of the current packet. 3) Bit 29(name: PauseEn). Writing a one (1) allows the transmit sequencer to stoppacket transmission, after completion of the current packet, wheneverthe receive sequencer detects an 802.3 X pause command packet. 4) Bit 28(name: LoadRng). Writing a one (1) causes the data in RcvAddrB[10:00] tobe loaded in to the Mac's random number register for use duringcollision back-offs. 5) Bits 27:20 (name: Reserved). 6) Bits 19:15(name: FreeQId). Selects the queue to which the freed buffer descriptorswill be written once the packet transmission has been terminated, eithersuccessfully or unsuccessfully. 7) Bits 14:10 (name: XmtQId). Selectsthe queue from which the transmit buffer descriptors will be fetched fordata packets. 8) Bits 09:05 (name: CtrlQId). Selects the queue fromwhich the transmit buffer descriptors will be fetched for controlpackets. These packets have transmission priority over the data packetsand will be exhausted before data packets will be transmitted. 9) Bits04:00 (name: VectQId). Selects the queue to which the transmit vectordata is written after the completion of each packet transmit. In someembodiments, transmit sequencer 2104 of FIG. 21 retrieves bufferdescriptors from two transmit queues, one of the queues having a highertransmission priority than the other. The higher transmission prioritytransmit queue is used for the transmission of TCP ACKs, whereas thelower transmission priority transmit queue is used for the transmissionof other types of packets. ACKs may be transmitted in accordance withtechniques set forth in U.S. patent application Ser. No. 09/802,426 (thesubject matter of which is incorporated herein by reference). In someembodiments, the processor that executes the Transmit FSM, the receiveand transmit sequencers, and the host processor that executes theprotocol stack are all realized on the same printed circuit board. Theprinted circuit board may, for example, be a card adapted for couplingto another computer.

[0142] All told, the above-described devices and systems for processingof data communication result in dramatic reductions in the time and hostresources required for processing large, connection-based messages.Protocol processing speed and efficiency is tremendously accelerated byspecially designed protocol processing hardware as compared with ageneral purpose CPU running conventional protocol software, andinterrupts to the host CPU are also substantially reduced. Theseadvantages can be provided to an existing host by addition of anintelligent network interface card (INIC), or the protocol processinghardware may be integrated with the CPU. In either case, the protocolprocessing hardware and CPU intelligently decide which device processesa given message, and can change the allocation of that processing basedupon conditions of the message.

DISCLOSURE FROM PROVISIONAL APPLICATION NO. 60/061,809

[0143] Background of the Invention.

[0144] Network processing as it exists today is a costly and inefficientuse of system resources. A 200 MHz Pentium-Pro is typically consumedsimply processing network data from a 100 Mb/second-network connection.The reasons that this processing is so costly are described here.

[0145] Too Many Data Moves.

[0146] When network packet arrives at a typical network interface card(NIC), the NIC moves the data into pre-allocated network buffers insystem main memory. From there the data is read into the CPU cache sothat it can be checksummed (assuming of course that the protocol in userequires checksums. Some, like IPX, do not.). Once the data has beenfully processed by the protocol stack, it can then be moved into itsfinal destination in memory. Since the CPU is moving the data, and mustread the destination cache line in before it can fill it and write itback out, this involves at a minimum two more trips across the systemmemory bus. In short, the best one can hope for is that the data willget moved across the system memory bus four times before it arrives inits final destination. It can, and does, get worse. If the data happensto get invalidated from system cache after it has been checksummed, thenit must get pulled back across the memory bus before it can be moved toits final destination. Finally, on some systems, including Windows NT4.0, the data gets copied yet another time while being moved up theprotocol stack. In NT 4.0, this occurs between the miniport driverinterface and the protocol driver interface. This can add up to awhopping eight trips across the system memory bus (the four tripsdescribed above, plus the move to replenish the cache, plus three moreto copy from the miniport to the protocol driver). That's enough tobring even today's advanced memory busses to their knees.

[0147] Too Much Processing by the CPU.

[0148] In all but the original move from the NIC to system memory, thesystem CPU is responsible for moving the data. This is particularlyexpensive because while the CPU is moving this data it can do nothingelse. While moving the data the CPU is typically stalled waiting for therelatively slow memory to satisfy its read and write requests. A CPU,which can execute an instruction every 5 nanoseconds, must now wait aslong as several hundred nanoseconds for the memory controller to respondbefore it can begin its next instruction. Even today's advancedpipelining technology doesn't help in these situations because thatrelies on the CPU being able to do useful work while it waits for thememory controller to respond. If the only thing the CPU has to lookforward to for the next several hundred instructions is more data moves,then the CPU ultimately gets reduced to the speed of the memorycontroller.

[0149] Moving all this data with the CPU slows the system down evenafter the data has been moved. Since both the source and destinationcache lines must be pulled into the CPU cache when the data is moved,more than 3 k of instructions and or data resident in the CPU cache mustbe flushed or invalidated for every 1500 byte frame. This is of courseassuming a combined instruction and data second level cache, as is thecase with the Pentium processors. After the data has been moved, theformer resident of the cache will likely need to be pulled back in,stalling the CPU even when we are not performing network processing.Ideally a system would never have to bring network frames into the CPUcache, instead reserving that precious commodity for instructions anddata that are referenced repeatedly and frequently.

[0150] But the data movement is not the only drain on the CPU. There isalso a fair amount of processing that must be done by the protocol stacksoftware. The most obvious expense is calculating the checksum for eachTCP segment (or UDP datagram). Beyond this, however, there is otherprocessing to be done as well. The TCP connection object must be locatedwhen a given TCP segment arrives, IP header checksums must becalculated, there are buffer and memory management issues, and finallythere is also the significant expense of interrupt processing which wewill discuss in the following section.

[0151] Too Many Interrupts.

[0152] A 64 k SMB request (write or read-reply) is typically made up of44 TCP segments when running over Ethernet (1500 byte MTU). Each ofthese segments may result in an interrupt to the CPU. Furthermore, sinceTCP must acknowledge all of this incoming data, it's possible to getanother 44 transmit-complete interrupts as a result of sending out theTCP acknowledgements. While this is possible, it is not terribly likely.Delayed ACK timers allow us to acknowledge more than one segment at atime. And delays in interrupt processing may mean that we are able toprocess more than one incoming network frame per interrupt.Nevertheless, even if we assume four incoming frames per input, and anacknowledgement for every two segments (as is typical per theACK-every-other-segment property of TCP), we are still left with 33interrupts per 64 k SMB request.

[0153] Interrupts tend to be very costly to the system. Often when asystem is interrupted, important information must be flushed orinvalidated from the system cache so that the interrupt routineinstructions, and needed data can be pulled into the cache. Since theCPU will return to its prior location after the interrupt, it is likelythat the information flushed from the cache will immediately need to bepulled back into the cache.

[0154] What's more, interrupts force a pipeline flush in today'sadvanced processors. While the processor pipeline is an extremelyefficient way of improving CPU performance, it can be expensive to getgoing after it has been flushed.

[0155] Finally, each of these interrupts results in expensive registeraccesses across the peripheral bus (PCI). This is discussed more in thefollowing section.

[0156] Inefficient Use of the Peripheral Bus (PCI).

[0157] We noted earlier that when the CPU has to access system memory,it may be stalled for several hundred nanoseconds. When it has to readfrom PCI, it may be stalled for many microseconds. This happens everytime the CPU takes an interrupt from a standard NIC. The first thing theCPU must do when it receives one of these interrupts is to read the NICInterrupt Status Register (ISR) from PCI to determine the cause of theinterrupt. The most troubling thing about this is that since interruptlines are shared on PC-based systems, we may have to perform thisexpensive PCI read even when the interrupt is not meant for us.

[0158] There are other peripheral bus inefficiencies as well. TypicalNICs operate using descriptor rings. When a frame arrives, the NIC readsa receive descriptor from system memory to determine where to place thedata. Once the data has been moved to main memory, the descriptor isthen written back out to system memory with status about the receivedframe. Transmit operates in a similar fashion. The CPU must notify thatNIC that it has a new transmit. The NIC will read the descriptor tolocate the data, read the data itself, and then write the descriptorback with status about the send. Typically on transmits the NIC willthen read the next expected descriptor to see if any more data needs tobe sent. In short, each receive or transmit frame results in 3 or 4separate PCI reads or writes (not counting the status register read).

[0159] Summary of the Invention.

[0160] Alacritech was formed with the idea that the network processingdescribed above could be offloaded onto a cost-effective IntelligentNetwork Interface Card (INIC). With the Alacritech INIC, we address eachof the above problems, resulting in the following advancements:

[0161] 1. The vast majority of the data is moved directly from the INICinto its final destination. A single trip across the system memory bus.

[0162] 2. There is no header processing, little data copying, and nochecksumming required by the CPU. Because of this, the data is nevermoved into the CPU cache, allowing the system to keep importantinstructions and data resident in the CPU cache.

[0163] 3. Interrupts are reduced to as little as 4 interrupts per 64 kSMB read and 2 per 64 k SMB write.

[0164] 4. There are no CPU reads over PCI and there are fewer PCIoperations per receive or transmit transaction.

[0165] In the remainder of this document we will describe how weaccomplish the above.

[0166] Perform Transport Level Processing on the INIC.

[0167] In order to keep the system CPU from having to process the packetheaders or checksum, the packet, we must perform this task on the INIC.This is a daunting task. There are more than 20,000 lines of C code thatmake up the FreeBSD TCP/IP protocol stack. Clearly this is more codethan could be efficiently handled by a competitively priced networkcard. Furthermore, as noted above, the TCP/IP protocol stack iscomplicated enough to consume a 200 MHz Pentium-Pro. Clearly in order toperform this function on an inexpensive card, we need special networkprocessing hardware as opposed to simply using a general purpose CPU.

[0168] Only Support TCP/IP.

[0169] In this section we introduce the notion of a “context”. A contextis required to keep track of information that spans many, possiblydiscontiguous, pieces of information. When processing TCP/IP data, thereare actually two contexts that must be maintained. The first context isrequired to reassemble IP fragments. It holds information about thestatus of the IP reassembly as well as any checksum information beingcalculated across the IP datagram (UDP or TCP). This context isidentified by the IP_ID of the datagram as well as the source anddestination IP addresses. The second context is required to handle thesliding window protocol of TCP. It holds information about whichsegments have been sent or received, and which segments have beenacknowledged, and is identified by the IP source and destinationaddresses and TCP source and destination ports.

[0170] If we were to choose to handle both contexts in hardware, wewould have to potentially keep track of many pieces of information. Onesuch example is a case in which a single 64 k SMB write is broken downinto 44 1500 byte TCP segments, which are in turn broken down into 131576 byte IP fragments, all of which can come in any order (though themaximum window size is likely to restrict the number of outstandingsegments considerably).

[0171] Fortunately, TCP performs a Maximum Segment Size negotiation atconnection establishment time, which should prevent IP fragmentation innearly all TCP connections. The only time that we should end up withfragmented TCP connections is when there is a router in the middle of aconnection which must fragment the segments to support a smaller MTU.The only networks that use a smaller MTU than Ethernet are serial lineinterfaces such as SLIP and PPP. At the moment, the fastest of theseconnections only run at 128 k (ISDN) so even if we had 256 of theseconnections, we would still only need to support 34 Mb/sec, or a littleover three 10 bT connections worth of data. This is not enough tojustify any performance enhancements that the INIC offers. If thisbecomes an issue at some point, we may decide to implement the MTUdiscovery algorithm, which should prevent TCP fragmentation on allconnections (unless an ICMP redirect changes the connection route whilethe connection is established).

[0172] With this in mind, it seems a worthy sacrifice to not attempt tohandle fragmented TCP segments on the INIC. UDP is another matter. SinceUDP does not support the notion of a Maximum Segment Size, it is theresponsibility of IP to break down a UDP datagram into MTU sizedpackets. Thus, fragmented UDP datagrams are very common. The most commonUDP application running today is NFSV2 over UDP. While this is also themost common version of NFS running today, the current version of Solarisbeing sold by Sun Microsystems runs NFSV3 over TCP by default. We canexpect to see the NFSV2/UDP traffic start to decrease over the comingyears. In summary, we will only offer assistance to non-fragmented TCPconnections on the INIC.

[0173] Don't Handle TCP “Exceptions”.

[0174] As noted above, we won't provide support for fragmented TCPsegments on the INIC.

[0175] We have also opted to not handle TCP connection and breakdown.Here is a list of other TCP “exceptions” which we have elected to nothandle on the INIC:

[0176] Fragmented Segments—Discussed above.

[0177] Retransmission Timeout—Occurs when we do not get anacknowledgement for previously sent data within the expected timeperiod.

[0178] Out of order segments—Occurs when we receive a segment with asequence number other than the next expected sequence number.

[0179] FIN segment—Signals the close of the connection.

[0180] Since we have now eliminated support for so many different codepaths, it might seem hardly worth the trouble to provide any assistanceby the card at all. This is not the case. According to W. RichardStevens and Gary Write in their book “TCP/IP Illustrated Volume 2”, TCPoperates without experiencing any exceptions between 97 and 100 percentof the time in local area networks. As network, router, and switchreliability improve this number is likely to only improve with time.

[0181] Two Modes of Operation.

[0182] So the next question is what to do about the network packets thatdo not fit our criteria. The answer shown in FIG. 24 is to use two modesof operation: One in which the network frames are processed on the INICthrough TCP and one in which the card operates like a typical dumb NIC.We call these two modes fast-path, and slow-path. In the slow-path case,network frames are handed to the system at the MAC layer and passed upthrough the host protocol stack like any other network frame. In thefast path case, network data is given to the host after the headers havebeen processed and stripped.

[0183] The transmit case works in much the same fashion. In slow-pathmode the packets are given to the INIC with all of the headers attached.The INIC simply sends these packets out as if it were a dumb NIC. Infast-path mode, the host gives raw data to the INIC which it must carveinto MSS sized segments, add headers to the data, perform checksums onthe segment, and then send it out on the wire.

[0184] The TCB Cache.

[0185] Consider a situation in which a TCP connection is being handledby the card and a fragmented TCP segment for that connection arrives. Inthis situation, it will be necessary for the card to turn control ofthis connection over to the host.

[0186] This introduces the notion of a Transmit Control Block (TCB)cache. A TCB is a structure that contains the entire context associatedwith a connection. This includes the source and destination IP addressesand source and destination TCP ports that define the connection. It alsocontains information about the connection itself such as the currentsend and receive sequence numbers, and the first-hop MAC address, etc.The complete set of TCBs exists in host memory, but a subset of thesemay be “owned” by the card at any given time. This subset is the TCBcache. The INIC can own up to 256 TCBs at any given time.

[0187] TCBs are initialized by the host during TCP connection setup.Once the connection has achieved a “steady-state” of operation, itsassociated TCB can then be turned over to the INIC, putting us intofast-path mode. From this point on, the INIC owns the connection untileither a FIN arrives signaling that the connection is being closed, oruntil an exception occurs which the INIC is not designed to handle (suchas an out of order segment). When any of these conditions occur, theINIC will then flush the TCB back to host memory, and issue a message tothe host telling it that it has relinquished control of the connection,thus putting the connection back into slow-path mode. From this pointon, the INIC simply hands incoming segments that are destined for thisTCB off to the host with all of the headers intact.

[0188] Note that when a connection is owned by the INIC, the host is notallowed to reference the corresponding TCB in host memory as it willcontain invalid information about the state of the connection.

[0189] TCP Hardware Assistance.

[0190] When a frame is received by the INIC, it must verify itcompletely before it even determines whether it belongs to one of itsTCBs or not. This includes all header validation (is it IP, IPV4 or V6,is the IP header checksum correct, is the TCP checksum correct, etc).Once this is done it must compare the source and destination IP addressand the source and destination TCP port with those in each of its TCBsto determine if it is associated with one of its TCBs. This is anexpensive process. To expedite this, we have added several features inhardware to assist us. The header is fully parsed by hardware and itstype is summarized in a single status word. The checksum is alsoverified automatically in hardware, and a hash key is created out of theIP addresses and TCP ports to expedite TCB lookup. For full details onthese and other hardware optimizations, refer to the INIC HardwareSpecification sections (Heading 8).

[0191] With the aid of these and other hardware features, much of thework associated with TCP is done essentially for free. Since the cardwill automatically calculate the checksum for TCP segments, we can passthis on to the host, even when the segment is for a TCB that the INICdoes not own.

[0192] TCP Summary.

[0193] By moving TCP processing down to the INIC we have offloaded thehost of a large amount of work. The host no longer has to pull the datainto its cache to calculate the TCP checksum. It does not have toprocess the packet headers, and it does not have to generate TCP ACKs.We have achieved most of the goals outlined above, but we are not doneyet.

[0194] Transport Layer Interface.

[0195] This section defines the INIC's relation to the hosts transportlayer interface (Called TDI or Transport Driver Interface in WindowsNT). For full details on this interface, refer to the Alacritech TCP(ATCP) driver specification (Heading 4).

[0196] Receive.

[0197] Simply implementing TCP on the INIC does not allow us to achieveour goal of landing the data in its final destination. Somehow the hosthas to tell the INIC where to put the data. This is a problem in thatthe host cannot do this without knowing what the data actually is.Fortunately, NT has provided a mechanism by which a transport driver can“indicate” a small amount of data to a client above it while telling itthat it has more data to come. The client, having then received enoughof the data to know what it is, is then responsible for allocating ablock of memory and passing the memory address or addresses back down tothe transport driver, which is in turn responsible for moving the datainto the provided location.

[0198] We will make use of this feature by providing a small amount ofany received data to the host, with a notification that we have moredata pending. When this small amount of data is passed up to the client,and it returns with the address in which to put the remainder of thedata, our host transport driver will pass that address to the INIC whichwill DMA the remainder of the data into its final destination.

[0199] Clearly there are circumstances in which this does not makesense. When a small amount of data (500 bytes for example), with a pushflag set indicating that the data must be delivered to the clientimmediately, it does not make sense to deliver some of the data directlywhile waiting for the list of addresses to DMA the rest. Under thesecircumstances, it makes more sense to deliver the 500 bytes directly tothe host, and allow the host to copy it into its final destination.While various ranges are feasible, it is currently preferred thatanything less than a segment's (1500 bytes) worth of data will bedelivered directly to the host, while anything more will be delivered asa small piece which may be 128 bytes, while waiting until receiving thedestination memory address before moving the rest.

[0200] The trick then is knowing when the data should be delivered tothe client or not. As we've noted, a push flag indicates that the datashould be delivered to the client immediately, but this alone is notsufficient. Fortunately, in the case of NetBIOS transactions (such asSMB), we are explicitly told the length of the session message in theNetBIOS header itself. With this we can simply indicate a small amountof data to the host immediately upon receiving the first segment. Theclient will then allocate enough memory for the entire NetBIOStransaction, which we can then use to DMA the remainder of the data intoas it arrives. In the case of a large (56 k for example) NetBIOS sessionmessage, all but the first couple hundred bytes will be DMA'd to theirfinal destination in memory.

[0201] But what about applications that do not reside above NetBIOS? Inthis case we can not rely on a session level protocol to tell us thelength of the transaction. Under these circumstances we will buffer thedata as it arrives until A) we have receive some predetermined number ofbytes such as 8 k, or B) some predetermined period of time passesbetween segments or C) we get a push flag. If after any of theseconditions occur we will then indicate some or all of the data to thehost depending on the amount of data buffered. If the data buffered isgreater than about 1500 bytes we must then also wait for the memoryaddress to be returned from the host so that we may then DMA theremainder of the data.

[0202] Transmit.

[0203] The transmit case is much simpler. In this case the client(NetBIOS for example) issues a TDI Send with a list of memory addresseswhich contain data that it wishes to send along with the length. Thehost can then pass this list of addresses and length off to the INIC.The INIC will then pull the data from its source location in hostmemory, as it needs it, until the complete TDI request is satisfied.

[0204] Affects on Interrupts.

[0205] Note that when we receive a large SMB transaction, for example,that there are two interactions between the INIC and the host. The firstin which the INIC indicates a small amount of the transaction to thehost, and the second in which the host provides the memory location(s)in which the INIC places the remainder of the data. This results in onlytwo interrupts from the INIC. The first when it indicates the smallamount of data and the second after it has finished filling in the hostmemory given to it. A drastic reduction from the 33/64 k SMB requestthat we estimate at the beginning of this section. On transmit, weactually only receive a single interrupt when the send command that hasbeen given to the INIC completes.

[0206] Transport Layer Interface Summary.

[0207] Having now established our interaction with Microsoft's TDIinterface, we have achieved our goal of landing most of our datadirectly into its final destination in host memory. We have also managedto transmit all data from its original location on host memory. Andfinally, we have reduced our interrupts to 2 per 64 k SMB read and 1 per64 k SMB write. The only thing that remains in our list of objectives isto design an efficient host (PCI) interface.

[0208] Host (PCI) Interface.

[0209] In this section we define the host interface. For a more detaileddescription, refer to the “Host Interface Strategy for the AlacritechINIC” section (Heading 3).

[0210] Avoid PCI Reads.

[0211] One of our primary objectives in designing the host interface ofthe INIC was to eliminate PCI reads in either direction. PCI reads areparticularly inefficient in that they completely stall the reader untilthe transaction completes. As noted above, this could hold a CPU up forseveral microseconds, a thousand times the time typically required toexecute a single instruction. PCI writes on the other hand, are usuallybuffered by the memory-bus

PCI-bridge allowing the writer to continue on with other instructions.This technique is known as “posting”.

[0212] Memory-Based Status Register.

[0213] The only PCI read that is required by most NICs is the read ofthe interrupt status register. This register gives the host CPUinformation about what event has caused an interrupt (if any). In thedesign of our INIC we have elected to place this necessary statusregister into host memory. Thus, when an event occurs on the INIC, itwrites the status register to an agreed upon location in host memory.The corresponding driver on the host reads this local register todetermine the cause of the interrupt. The interrupt lines are held highuntil the host clears the interrupt by writing to the INIC's InterruptClear Register. Shadow registers are maintained on the INIC to ensurethat events are not lost.

[0214] Buffer Addresses are Pushed to the INIC.

[0215] Since it is imperative that our INIC operate as efficiently aspossible, we must also avoid PCI reads from the INIC. We do this bypushing our receive buffer addresses to the INIC. As mentioned at thebeginning of this section, most NICs work on a descriptor queuealgorithm in which the NIC reads a descriptor from main memory in orderto determine where to place the next frame. We will instead writereceive buffer addresses to the INIC as receive buffers are filled. Inorder to avoid having to write to the INIC for every receive frame, weinstead allow the host to pass off a pages worth (4 k) of buffers in asingle write.

[0216] Support Small and Large Buffers on Receive.

[0217] In order to reduce further the number of writes to the INIC, andto reduce the amount of memory being used by the host, we support twodifferent buffer sizes. A small buffer contains roughly 200 bytes ofdata payload, as well as extra fields containing status about thereceived data bringing the total size to 256 bytes. We can thereforepass 16 of these small buffers at a time to the INIC. Large buffers are2 k in size. They are used to contain any fast or slow-path data thatdoes not fit in a small buffer. Note that when we have a large fast-pathreceive, a small buffer will be used to indicate a small piece of thedata, while the remainder of the data will be DMA'd directly intomemory. Large buffers are never passed to the host by themselves,instead they are always accompanied by a small buffer which containsstatus about the receive along with the large buffer address. Byoperating in the manner, the driver must only maintain and process thesmall buffer queue. Large buffers are returned to the host by virtue ofbeing attached to small buffers. Since large buffers are 2 k in sizethey are passed to the INIC 2 buffers at a time.

[0218] Command and Response Buffers.

[0219] In addition to needing a manner by which the INIC can passincoming data to us, we also need a manner by which we can instruct theINIC to send data. Plus, when the INIC indicates a small amount of datain a large fast-path receive, we need a method of passing back theaddress or addresses in which to put the remainder of the data. Weaccomplish both of these with the use of a command buffer. Sadly, thecommand buffer is the only place in which we must violate our rule ofonly pushing data across PCI. For the command buffer, we write theaddress of command buffer to the INIC. The INIC then reads the contentsof the command buffer into its memory so that it can execute the desiredcommand. Since a command may take a relatively long time to complete, itis unlikely that command buffers will complete in order. For this reasonwe also maintain a response buffer queue. Like the small and largereceive buffers, a page worth of response buffers is passed to the INICat a time. Response buffers are only 32 bytes, so we have to replenishthe INIC's supply of them relatively infrequently. The response buffersonly purpose is to indicate the completion of the designated commandbuffer, and to pass status about the completion.

EXAMPLES

[0220] In this section we will provide a couple of examples describingsome of the differing data flows that we might see on the AlacritechINIC.

[0221] Fast-Path 56 K NetBIOS Session Message.

[0222] Let's say a 56 k NetBIOS session message is received on the INIC.The first segment will contain the NetBIOS header, which contains thetotal NetBIOS length. A small chunk of this first segment is provided tothe host by filling in a small receive buffer, modifying the interruptstatus register on the host, and raising the appropriate interrupt line.Upon receiving the interrupt, the host will read the ISR, clear it bywriting back to the INIC's Interrupt Clear Register, and will thenprocess its small receive buffer queue looking for receive buffers to beprocessed. Upon finding the small buffer, it will indicate the smallamount of data up to the client to be processed by NetBIOS. It willalso, if necessary, replenish the receive buffer pool on the INIC bypassing off a pages worth of small buffers. Meanwhile, the NetBIOSclient will allocate a memory pool large enough to hold the entireNetBIOS message, and will pass this address or set of addresses down tothe transport driver. The transport driver will allocate an INIC commandbuffer, fill it in with the list of addresses, set the command type totell the INIC that this is where to put the receive data, and then passthe command off to the INIC by writing to the command register. When theINIC receives the command buffer, it will DMA the remainder of theNetBIOS data, as it is received, into the memory address or addressesdesignated by the host. Once the entire NetBIOS transaction is complete,the INIC will complete the command by writing to the response bufferwith the appropriate status and command buffer identifier.

[0223] In this example, we have two interrupts, and all but a couplehundred bytes are DMA'd directly to their final destination. On PCI wehave two interrupt status register writes, two interrupt clear registerwrites, a command register write, a command read, and a response bufferwrite.

[0224] With a standard NIC this would result in an estimated 30interrupts, 30 interrupt register reads, 30 interrupt clear writes, and58 descriptor reads and writes. Plus the data will get moved anywherefrom 4 to 8 times across the system memory bus.

[0225] Slow-Path Receive.

[0226] If the INIC receives a frame that does not contain a TCP segmentfor one of its TCB's, it simply passes it to the host as if it were adumb NIC. If the frame fits into a small buffer (˜200 bytes or less),then it simply fills in the small buffer with the data and notifies thehost. Otherwise it places the data in a large buffer, writes the addressof the large buffer into a small buffer, and again notifies the host.The host, having received the interrupt and found the completed smallbuffer, checks to see if the data is contained in the small buffer, andif not, locates the large buffer. Having found the data, the host willthen pass the frame upstream to be processed by the standard protocolstack. It must also replenish the INIC's small and large receive bufferpool if necessary.

[0227] With the INIC, this will result in one interrupt, one interruptstatus register write and one interrupt clear register write as well asa possible small and or large receive buffer register write. The datawill go through the normal path although if it is TCP data then the hostwill not have to perform the checksum.

[0228] With a standard NIC this will result in a single interrupt, aninterrupt status register read, an interrupt clear register write, and adescriptor read and write. The data will get processed as it would bythe INIC, except for a possible extra checksum.

[0229] Fast-Path 400 Byte Send.

[0230] In this example, lets assume that the client has a small amountof data to send. It will issue the TDI Send to the transport driverwhich will allocate a command buffer, fill it in with the address of the400 byte send, and set the command to indicate that it is a transmit. Itwill then pass the command off to the INIC by writing to the commandregister. The INIC will then DMA the 400 bytes into its own memory,prepare a frame with the appropriate checksums and headers, and send theframe out on the wire. After it has received the acknowledgement it willthen notify the host of the completion by writing to a response buffer.

[0231] With the INIC, this will result in one interrupt, one interruptstatus register write, one interrupt clear register write, a commandbuffer register write a command buffer read, and a response bufferwrite. The data is DMA'd directly from the system memory.

[0232] With a standard NIC this will result in a single interrupt, aninterrupt status register read, an interrupt clear register write, and adescriptor read and write. The data would get moved across the systembus a minimum of 4 times. The resulting TCP ACK of the data, however,would add yet another interrupt, another interrupt status register read,interrupt clear register write, a descriptor read and write, and yetmore processing by the host protocol stack.

[0233] Host Interface Strategy for the Alacritech INIC.

[0234] This section describes the host interface strategy for theAlacritech Intelligent Network Interface Card (INIC). The goal of theAlacritech INIC is to not only process network data through TCP, butalso to provide zero-copy support for the SMP upper-layer protocol. Itachieves this by supporting two paths for sending and receiving data,the fast-path and the slow-path. The fast path data flow corresponds toconnections that are maintained on the NIC, while slow-path trafficcorresponds to network data for which the NIC does not have aconnection. The fast-path flow works by passing a header to the host andsubsequently holding further data for that connection on the card untilthe host responds via an INIC command with a set of buffers into whichto place the accumulated data. In the slow-path data flow, the INIC willbe operating as a “dumb” NIC, so that these packets are simply dumpedinto frame buffers on the host as they arrive. To do either pathrequires a pool of smaller buffers to be used for headers and a pool ofdata buffers for frames/data that are too large for the header buffer,with both pools being managed by the INIC. This section discusses howthese two pools of data are managed as well as how buffers areassociated with a given context.

[0235] Receive Interface.

[0236] The varying requirements of the fast and slow paths and a desireto save PCI bandwidth are the driving forces behind the host interfacethat is described herein. As mentioned above, the fast-path flow puts aheader into a header buffer that is then forwarded to the host. The hostuses the header to determine what further data is following, allocatesthe necessary host buffers, and these are passed back to the INIC via acommand to the INIC. The INIC then fills these buffers from data it wasaccumulating on the card and notifies the host by sending a response tothe command. Alternatively, the fast-path may receive a header and datathat is a complete request, but that is also too large for a headerbuffer. This results in a header and data buffer being passed to thehost. This latter flow is identical to the slow-path flow, which alsoputs all the data into the header buffer or, if the header is too small,uses a large (2 K) host buffer for all the data. This means that on theunsolicited receive path, the host will only see either a header bufferor a header and at most, one data buffer. Note that data is never splitbetween a header and a data buffer.

[0237]FIG. 25 illustrates both situations. Since we want to fill in theheader buffer with a single DMA, the header must be the last piece ofdata to be written to the host for any received transaction.

[0238] Receive Interface Details.

[0239] Header Buffers.

[0240] Header buffers in host memory are 256 bytes long, and are alignedon 256 byte boundaries. There will be a field in the header bufferindicating it has valid data. This field will initially be reset by thehost before passing the buffer descriptor to the INIC. A set of headerbuffers are passed from the host to the INIC by the host writing to the“Header Buffer Address Register” on the INIC. This register is definedas follows: Bits 31-8 Physical address in host memory of the first of aset of contiguous header buffers. Bits 7-0 Number of header bufferspassed.

[0241] In this way the host can, say, allocate 16 buffers in a 4 K page,and pass all 16 buffers to the INIC with one register write. The INICwill maintain a queue of these header descriptors in the SmallHTypequeue in it's own local memory, adding to the end of the queue everytime the host writes to the Header Buffer Address Register. Note thatthe single entry is added to the queue; the eventual dequeuer will usethe count after extracting that entry.

[0242] The header buffers, will be used and returned to the host in thesame order that they were given to the INIC. The valid field will be setby the INIC before returning the buffer to the host. In this way a PCIinterrupt, with a single bit in the interrupt register, may be generatedto indicate that there is a header buffer for the host to process. Whenservicing this interrupt, the host will look at its queue of headerbuffers, reading the valid field to determine how many header buffersare to be processed.

[0243] Receive Data Buffers.

[0244] Receive data buffers in host memory are aligned to pageboundaries, assumed here to be 2 K bytes long and aligned on 4 K pageboundaries, 2 buffers per page. In order to pass receive data buffers tothe INIC, the host must write to two registers on the INIC. The firstregister to be written is the “Data Buffer Handle Register.” The bufferhandle is not significant to the INIC, but will be copied back to thehost to return the buffer to the host. The second register written isthe Data Buffer Address Register. This is the physical address of thedata buffer. When both registers have been written, the INIC will addthe contents of these two registers to FreeType queue of data bufferdescriptors. Note that the INIC host driver sets the handle registerfirst, then the address register. There needs to be some mechanism putin place to ensure the reading of these registers does not get out ofsync with writing them. Effectively the INIC can read the addressregister first and save its contents, then read the handle register. Itcan then lock the register pair in some manner such that another writeto the handle register is not permitted until the current contents havebeen saved. Both addresses extracted from the registers are to bewritten to the FreeType queue. The INIC will extract 2 entries each timewhen dequeuing.

[0245] Data buffers will be allocated and used by the INIC as needed.For each data buffer used by a slow-path transaction, the data bufferhandle will be copied into a header buffer. Then the header buffer willbe returned to the host.

[0246] Transmit Interface.

[0247] Transmit Interface Overview.

[0248] The transmit interface shown in FIG. 26, like the receiveinterface, has been designed to minimize the amount of PCI bandwidth andlatencies. In order to transmit data, the host will transfer a commandbuffer to the INIC. This command buffer will include a command bufferhandle, a command field, possibly a TCP context identification, and alist of physical data pointers. The command buffer handle is defined tobe the first word of the command buffer and is used by the host toidentify the command. This word will be passed back to the host in aresponse buffer, since commands may complete out of order, and the hostwill need to know which command is complete. Commands will be used formany reasons, but primarily to cause the INIC to transmit data, or topass a set of buffers to the INIC for input data on the fast-path aspreviously discussed.

[0249] Response buffers are physical buffers in host memory. They areused by the INIC in the same order as they were given to it by the host.This enables the host to know which response buffer(s) to next look atwhen the INIC signals a command completion.

[0250] Transmit Interface Details.

[0251] Command Buffers.

[0252] Command buffers in host memory are a multiple of 32 bytes, up toa maximum of 1 K bytes, and are aligned on 32 byte boundaries. A commandbuffer is passed to the INIC by writing to one of five “Command BufferAddress Registers.” These registers are defined as follows: Bits 31-5Physical address in host memory of the command buffer. Bits 4-0 Lengthof command buffer in bytes/32 (i.e. number of multiples of 32 bytes).

[0253] This is the physical address of the command buffer. The registerto which the command is written predetermines the XMT interface number,or if the command is for the RCV CPU; hence there will be 5 of them, 0-3for XMT and 4 for RCV. When one of these registers has been written, theINIC will add the contents of the register to it's own internal queue ofcommand buffer descriptors. The first word of all command buffers isdefined to be the command buffer handle. It is the job of the utilityCPU to extract a command from its local queue, DMA the command into asmall INIC buffer (from the FreeSType queue), and queue that buffer intothe Xmit#Type queue, where # is 0-3 depending on the interface, or theappropriate RCV queue. The receiving CPU will service the queues toperform the commands. When that CPU has completed a command, it extractsthe command buffer handle and passes it back to the host via a responsebuffer.

[0254] Response Buffers.

[0255] Response buffers in host memory are 32 bytes long and aligned on32 byte boundaries. They are handled in a very similar fashion to headerbuffers. There will be a field in the response buffer indicating it hasvalid data. This field will initially be reset by the host beforepassing the buffer descriptor to the INIC. A set of response buffers arepassed from the host to the INIC by the host writing to the “ResponseBuffer Address Register” on the INIC. This register is defined asfollows: Bits 31-8 Physical address in host memory of the first of a setof contiguous response buffers. Bits 7-0 Number of response bufferspassed.

[0256] In this way the host can, say, allocate 128 buffers in a 4 Kpage, and pass all 128 buffers to the INIC with one register write. TheINIC will maintain a queue of these header descriptors in it'sResponseType queue, adding to the end of the queue every time the hostwrites to the “Response Buffer Address Register”. The INIC writes theextracted contents including the count, to the queue in exactly the samemanner as for the header buffers.

[0257] The response buffers can be used and returned to the host in thesame order that they were given to the INIC. The valid field will be setby the INIC before returning the buffer to the host. In this way a PCIinterrupt, with a single bit in the interrupt register, may be generatedto indicate that there is a response buffer for the host to process.When servicing this interrupt, the host will look at its queue ofresponse buffers, reading the valid field to determine how many responsebuffers are to be processed.

[0258] Interrupt Status Register/Interrupt Mask Register.

[0259]FIG. 27 shows the general format of this register. The setting ofany bits in the ISR will cause an interrupt, provided the correspondingbit in the Interrupt Mask Register is set. The default setting for theIMR is 0.

[0260] The INIC is configured so that the host should never need todirectly read the ISR from the INIC. To support this, it is importantfor the host/INIC to arrange a buffer area in host memory into which theISR is dumped. The address and size of that area ca be passed to theINIC via a command on the XMT interface. That command will also specifythe setting for the IMR. Until the INIC receives this command, it willnot DMA the ISR to host memory, and no events will cause an interrupt.The host could if necessary, read the ISR directly from the INIC in thiscase.

[0261] For the host to never have to actually read the register from theINIC itself, it is necessary for the INIC to update this host copy ofthe register whenever anything in it changes.

[0262] The host will Ack (or deassert) events in the register by writingthe register with 0's in appropriate bit fields. So that the host doesnot miss events, the following scheme has been developed:

[0263] The INIC keeps a local copy of the register whenever it DMAs itto the host i.e. after some event(s). Call this COPYA Then the INICstarts accumulating any new events not reflected in the host copy in aseparate word. Call this NEWA. As the host clears bits by writing theregister back with those bits set to zero, the INIC clears these bits inCOPYA (or the host write-back goes directly to COPYA). If there are newevents in NEWA, it ORs them with COPYA, and DMAs this new ISR to thehost. This new ISR then replaces COPYA, NEWA is cleared and the cyclethen repeats.

[0264] Register Address.

[0265] For the sake of simplicity, in this example of FIG. 28 theregisters are at 4-byte increments from whatever the base address is.

[0266] Alacritech TCP (ATCP) Design Specification.

[0267] This section outlines the design specification for the AlacritechTCP (ATCP) transport driver. The ATCP driver consists of threecomponents:

[0268] 1. The bulk of the protocol stack is based on the FreeBSD TCP/IPprotocol stack. This code performs the Ethernet, ARP, IP, ICMP, and(slow path) TCP processing for the driver.

[0269] 2. At the top of the protocol stack we introduce an NT filterdriver used to intercept TDI requests destined for the Microsoft TCPdriver.

[0270] 3. At the bottom of the protocol stack we include an NDISprotocol-driver interface which allows us to communicate with the INICminiport NDIS driver beneath the ATCP driver.

[0271] This section covers each of these topics, as well as issuescommon to the entire ATCP driver.

[0272] Coding Style.

[0273] In order to ensure that our ATCP driver is written in aconsistent manner, we have adopted a set of coding guidelines. Theseguidelines are introduced with the philosophy that we should write codein a Microsoft style since we are introducing an NT-based product. Theguidelines below apply to all code that we introduce into our driver.Since a very large portion of our ATCP driver will be based on FreeBSD,and since we are somewhat time-constrained on our driver development,the ported FreeBSD code will be exempt from these guidelines.

[0274] 1. Global symbols—All function names and global variables in theATCP driver should begin with the “ATK” prefix (ATKSend( ) forinstance).

[0275] 2. Variable names—Microsoft seems to use capital letters toseparate multi-word variable names instead of underscores (VariableNameinstead of variable_name). We should adhere to this style.

[0276] 3. Structure pointers—Microsoft typedefs all of their structures.The structure types are always capitals and they typedef a pointer tothe structure as “P”<name> as follows: typedef struct_FOO { INT bar; }FOO, *PFOO;

[0277] We will adhere to this style.

[0278] 4. Function calls—Microsoft separates function call arguments onseparate lines: X = foobar( argument1, argument2, );

[0279] We will adhere to this style.

[0280] 5. Comments—While Microsoft seems to alternatively use // and/**/ comment notation, we will exclusively use the /**/ notation.

[0281] 6. Function comments—Microsoft includes comments with eachfunction that describe the function, its arguments, and its returnvalue. We will also include these comments, but will move them fromwithin the function itself to just prior to the function for betterreadability.

[0282] 7. Function arguments—Microsoft includes the keywords IN and OUTwhen defining function arguments. These keywords denote whether thefunction argument is used as an input parameter, or alternatively as aplaceholder for an output parameter. We will include these keywords.

[0283] 8. Function prototypes—We will include function prototypes in themost logical header file corresponding to the .c file. For example, theprototype for function foo( ) found in foo.c will be placed in foo.h.

[0284] 9. Indentation—Microsoft code fairly consistently uses a tabstopof 4. We will do likewise.

[0285] 10. Header file #ifndef—each header file should contain a#ifndef/#define/#endif which is used to prevent recursive header fileincludes. For example, foo.h would include: #ifndef_FOO_H_(—)#define_FOO_H_(—) <foo.h contents..> #endif/*_FOO_H_*/ Notethe_NAME_H_format.

[0286] 11. Each file must contain a comment at the beginning whichincludes the $Id$ as follows: /* * $Id$ */

[0287] CVS (RCS) will expand this keyword to denote RCS revision,timestamps, author, etc.

[0288] SMP

[0289] This section describes the process by which we will make the ATCPdriver SMP safe. The basic rule for SMP kernel code is that any accessto a memory variable must be protected by a lock that prevents acompeting access by code running on another processor. Spinlocks are thenormal locking method for code paths which do not take a long time toexecute (and which do not sleep.)

[0290] In general each instance of a structure will include a spinlock,which must be acquired before members of that structure are accessed,and held while a function is accessing that instance of the structure.Structures which are logically grouped together may be protected by asingle spinlock: for example, the ‘in_pcb’ structure, ‘tcpcb’ structure,and ‘socket’ structure which together constitute the administrativeinformation for a TCP connection will probably be collectively managedby a single spinlock in the ‘socket’ structure.

[0291] In addition, every global data structure such as a list or hashtable must also have a protecting spinlock which must be held while thestructure is being accessed or modified. The NT DDK in fact provides anumber of convenient primitives for SMP-safe list manipulation, and itis recommended that these be used for any new lists. Existing listmanipulations in the FreeBSD code can probably be left as-is to minimizecode disturbance, except of course that the necessary spinlockacquisition and release must be added around them.

[0292] Spinlocks should not be held for long periods of time, and mostespecially, must not be held during a sleep, since this will lead todeadlocks. There is a significant deficiency in the NT kernel supportfor SMP systems: it does not provide an operation which allows aspinlock to be exchanged atomically for a sleep lock. This would be aserious problem in a UNIX environment where much of the processingoccurs in the context of the user process which initiated the operation.(The spinlock would have to be explicitly released, followed by aseparate acquisition of the sleep lock: creating an unsafe window.)

[0293] The NT approach is more asynchronous, however: IRPs are simplymarked as ‘PENDING’ when an operation cannot be completed immediately.The calling thread does NOT sleep at that point: it returns, and may goon with other processing. Pending IRPs are later completed, not bywaking up the thread which initiated them, but by an “IoCompleteRequest”call which typically runs at DISPATCH level in an arbitrary context.

[0294] Thus we have not in fact used sleep locks anywhere in the designof the ATCP driver, hoping the above issue will not arise.

[0295] Data Flow Overview.

[0296] The ATCP driver supports two paths for sending and receivingdata, the fast-path and the slow-path. The fast-path data flowcorresponds to connections that are maintained on the INIC, whileslow-path traffic corresponds to network data for which the INIC doesnot have a connection. In order to set some groundwork for the rest ofthis section, these two data paths are summarized here.

[0297] Fast-Path Input Data Flow.

[0298] There are 2 different cases to consider:

[0299] 1. NETBIOS traffic (identifiable by port number.)

[0300] 2. Everything else.

[0301] NetBIOS Input.

[0302] As soon as the INIC has received a segment containing a NETBIOSheader, it will forward it up to the TCP driver, along with the NETBIOSlength from the header. (In principle the host could get this from theheader itself, but since the INIC has already done the decode, it seemreasonable to just pass it.)

[0303] From the TDI spec, the amount of data in the buffer actually sentmust be at least 128 bytes. For small SMBs, all of the received SMBshould be forwarded; it will be absorbed directly by the TDI clientwithout any further MDL exchange. Experiments tracing the TDI data flowshow that the NETBIOS client directly absorbs up to 1460 bytes: theamount of payload data in a single Ethernet frame. Thus the initialsystem specifies that the INIC will indicate anything up to a completesegment to the ATCP driver. [See note (1)].

[0304] Once the INIC has passed up an indication with an NETBIOS lengthgreater than the amount of data in the packet it passed, it willcontinue to accumulate further incoming data in DRAM on the INIC.Overflow of INIC DRAM buffers will be avoided by using a receive windowon the INIC at this point, which can be 8 K.

[0305] On receiving the indicated packet, the ATCP driver will call thereceive handler registered by the TDI client for the connection, passingthe actual size of the data in the packet from the INIC as “bytesindicated” and the NETBIOS length as “bytes available.” [See note (2)].

[0306] In the “large data input” case, where “bytes available” exceedsthe packet length, the TDI client will then provide an MDL, associatedwith an IRP, which must be completed when this MDL is filled. (ThisIRP/MDL may come back either in the response to TCP's call of thereceive handler, or as an explicit TDI_RECEIVE request.)

[0307] The ATCP driver will build a “receive request” from the MDLinformation, and pass this to the INIC. This request will contain:

[0308] 1) The TCP context identifier; 2) Size and offset information; 3)A list of physical addresses corresponding to the MDL pages; 4) Acontext field to allow the ATCP driver to identify the request oncompletion; and 5) “Piggybacked” window update information.

[0309] Note: the ATCP driver must copy any remaining data (which was nottaken by the receive handler) from the segment indicated by the INIC tothe start of the MDL, and must adjust the size & offset information inthe request passed to the INIC to account for this.

[0310] The INIC will fill the given page(s) with incoming data up to therequested amount, and respond to the ATCP driver when this is done [Seenote (3)]. If the MDL is large, the INIC may open up its advertisedreceive window for improved throughput while filling the MDL. Onreceiving the response from the INIC, the ATCP driver will complete theIRP associated with this MDL, to tell the TDI client that the data isavailable. At this point the cycle of events is complete, and the ATCPdriver is now waiting for the next header indication.

[0311] Other TCP Input.

[0312] In the general case we do not have a higher-level protocol headerto enable us to predict that more data is coming. So on non-NETBIOSconnections, the INIC will just accumulate incoming data in INIC DRAM upto a quantity of 8 K in this example. Again, a maximum advertised windowsize, which may be 16 K, will be used to prevent overflow of INIC DRAMbuffers.

[0313] When the prescribed amount has been accumulated, or when a PSHflag is seen, the INIC will indicate a small packet which may be 128bytes of the data to the ATCP driver, along with the total length of thedata accumulated in INIC DRAM.

[0314] On receiving the indicated packet, the ATCP driver will call thereceive handler registered by the TDI client for the connection, passingthe actual size of the data in the packet from the INIC as “bytesindicated” and the total INIC-buffer length as “bytes available.”

[0315] As in the NETBIOS case, if “bytes available” exceeds “bytesindicated”, the TDI client will provide an IRP with an MDL. The ATCPdriver will pass the MDL to the INIC to be filled, as before. The INICwill reply to the ATCP driver, which in turn will complete the IRP tothe TDI client.

[0316] Using an MDL from the client avoids a copy step. However, if wecan only buffer 8 K and delay indicating to the ATCP driver until wehave done so, a question arises regarding further segments coming in,since INIC DRAM is a scarce resource. We do not want to ACK with azero-size window advertisement: this would cause the transmitting end togo into persist state, which is bad for throughput. If the transmittingend is also our INIC, this results in having to implement the persisttimer on the INIC, which we do not wish to do. Instead for largetransfers (i.e. no PSH flag seen) we will not send an ACK until the hosthas provided the MDL, and also, to avoid stopping the transmitting end,we will use a receive window of twice the amount we will buffer beforecalling the host. Since the host comes back with the MDL quite quickly(measured at <100 microseconds), we do not expect to experiencesignificant overruns.

[0317] INIC Receive Window Updates.

[0318] If the INIC “owns” an MDL provided by the TDI client (sent byATCP as a receive request), it will treat this as a “promise” by the TDIclient to accept the data placed in it, and may therefore ACK incomingdata as it is filling the pages.

[0319] However, for small requests, there will be no MDL returned by theTDI client: it absorbs all of the data directly in the receive callbackfunction. We need to update the INIC's view of data which has beenaccepted, so that it can update its receive window. In order to be ableto do this, the ATCP driver will accumulate a count of data which hasbeen accepted by the TDI client receive callback function for aconnection.

[0320] From the INIC's point of view, though, segments sent up to theATCP driver are just “thrown over the wall”; there is no explicit replypath. We will therefore “piggyback” the update on requests sent out tothe INIC. Whenever the ATCP driver has outgoing data for thatconnection, it will place this count in a field in the send request (andthen clear the counter.) Any receive request (passing a receive MDL tothe INIC) may also be used to transport window update info in the sameway.

[0321] Note: we will probably also need to design a message path wherebythe ATCP driver can explicitly send an update of this “bytes consumed”information (either when it exceeds a preset threshold or if there areno requests going out to the INIC for more than a given time interval),to allow for possible scenarios in which the data stream is entirelyone-way.

[0322] Notes.

[0323] 1) The PSH flag can help to identify small SMB requests that fitinto one segment.

[0324] 2) Actually, the observed “bytes available” from the NT TCPdriver to its client's callback in this case is always 1460. TheNETBIOS-aware TDI client presumably calculates the size of the MDL itwill return from the NETBIOS header. So strictly speaking we do not needthe NETBIOS header length at this point: just an indication that this isa header for a “large” size. However, we *do* need an actual “bytesavailable” value for the non-NETBIOS case, so we may as well pass it.

[0325] 3) We observe that the PSH flag is set in the segment completingeach NETBIOS transfer. The INIC can use this to determine when thecurrent transfer is complete and the MDL should be returned. It can, atleast in a debug mode, sanity check the amount of received data againstwhat is expected, though.

[0326] Fast-Path Output Data Flow.

[0327] The fast-path output data flow is similar to the input data-flow,but simpler. In this case the TDI client will provide a MDL to the ATCPdriver along with an IRP to be completed when the data is sent. The ATCPdriver will then give a request (corresponding to the MDL) to the INIC.This request will contain:

[0328] 1) The TCP context identifier; 2) Size and offset information; 3)A list of physical addresses corresponding to the MDL pages; 4) Acontext field to allow the ATCP driver to identify the request oncompletion; 5) “Piggybacked” window update information (as discussed insection 6.1.3.)

[0329] The INIC will copy the data from the given physical location(s)as it sends the corresponding network frames onto the network. When allof the data is sent, the INIC will notify the host of the completion,and the ATCP driver will complete the IRP.

[0330] Note that there may be multiple output requests pending at anygiven time, since SMB allows multiple SMB requests to be simultaneouslyoutstanding.

[0331] Slow-Path Data Flow.

[0332] For data for which there is no connection being maintained on theINIC, we will have to perform all of the TCP, IP, and Ethernetprocessing ourselves. To accomplish this we will port the FreeBSDprotocol stack. In this mode, the INIC will be operating as a “dumbNIC”; the packets which pass over the NDIS interface will just containMAC-layer frames.

[0333] The MBUFs in the incoming direction will in fact be managingNDIS-allocated packets. In the outgoing direction, we needprotocol-allocated MBUFs in which to assemble the data and headers. TheMFREE macro must be cognizant of the various types of MBUFs, and “do theright thing” for each type.

[0334] We will retain a (modified) socket structure for each connection,containing the socket buffer fields expected by the FreeBSD code. TheTCP code that operates on socket buffers (adding/removing MBUFs to &from queues, indicating acknowledged & received data etc) will remainessentially unchanged from the FreeBSD base (though most of the socketfunctions & macros used to do this will need to be modified; these arethe functions in kem/uipc_socket2.c)

[0335] The upper socket layer (kern/uipc_socket.c), where the overlyingOS moves data in and out of socket buffers, must be entirelyre-implemented to work in TDI terms. Thus, instead of sosend( ), therewill be a function that copies data from the MDL provided in a TDI_SENDcall into socket buffer MBUFs. Instead of soreceive( ), there will be ahandler that calls the TDI client receive callback function, and alsocopies data from socket buffer MBUFs into any MDL provided by the TDIclient (either explicitly with the callback response or as a separateTDI_RECEIVE call.)

[0336] We must note that there is a semantic difference between TDI_SENDand a write( ) on a BSD socket. The latter may complete back to itscaller as soon as the data has been copied into the socket buffer. Thecompletion of a TDI_SEND, however, implies that the data has actuallybeen sent on the connection. Thus we will need to keep the TDI_SEND IRPs(and associated MDLs) in a queue on the socket until the TCP codeindicates that the data from them has been ACK'd.

[0337] Data Path Notes:

[0338] 1. There might be input data on a connection object for whichthere is no receive handler function registered. This has not beenobserved, but we can probably just ASSERT for a missing handler for themoment. If it should happen, however, we must assume that the TDI clientwill be doing TDI RECEIVE calls on the connection. If we can't make acallup at the time that the indication from the INIC appears, we canqueue the data and handle it when a TDI_RECEIVE does appear.

[0339] 2. NT has a notion of “canceling” IRPs. It is possible for us toget a “cancel” on an IRP corresponding to an MDL which has been “handed”to the INIC by a send or receive request. We can handle this by beingable to force the context back off the INIC, since IRPs will only getcancelled when the connection is being aborted.

[0340] Context Passing between ATCP and INIC. from ATCP to INIC.

[0341] There is a synchronization problem that must be addressed here.The ATCP driver will make a decision on a given connection that thisconnection should now be passed to the INIC. It builds and sends acommand identifying this connection to the INIC.

[0342] Before doing so, it must ensure that no slow-path outgoing datais outstanding. This is not difficult; it simply pends and queues anynew TDI_SEND requests and waits for any unacknowledged slow path outputdata to be acknowledged before initiating the context pass operation.

[0343] The problem arises with incoming slow-path data. If we attempt todo the context-pass in a single command handshake, there is a windowduring which the ATCP driver has send the context command, but the INIChas not yet seen this (or has not yet completed setting up its context.)During this time, slow-path input data frames could arrive and be fedinto the slow-path ATCP processing code. Should that happen, the contextinformation which the ATCP driver passed to the INIC is no longercorrect. We can simply abort the outward pass of the context in thisevent, but it seems better to have a reliable handshake.

[0344] Therefore, the command to pass context from ATCP driver to INICwill be split into two halves, and there will be a two-exchangehandshake.

[0345] The initial command from ATCP to INIC expresses an “intention” tohand out the context. It will include the source and destination IPaddresses and ports, which will allow the INIC to establish a“provisional” context. Once it has this “provisional” context in place,the INIC will not send any more slow-path input frames for that src/destIP/port combination (it will queue them, if any are received.)

[0346] When the ATCP driver receives the response to this initial“intent” command, it knows that the INIC will send no more slow-pathinput. The ATCP driver then waits for any remaining unconsumed slow-pathinput data for this connection to be consumed by the client. (Generallyspeaking there will be none, since the ATCP driver will not initiate acontext pass while there is unconsumed slow-path input data; thehandshake is simply to close the crossover window.)

[0347] Once any such data has been consumed, we know things are in aquiescent state. The ATCP driver can then send the second, “commit”command to hand out the context, with confidence that the TCB values itis handing out (sequence numbers etc) are reliable.

[0348] Note 1: it is conceivable that there might be situations in whichthe ATCP driver decides, after having sent the original “intention”command, that the context is not to be passed after all. (E.g. the localclient issues a close.) So we must allow for the possibility that thesecond command may be a “abort”, which should cause the INIC todeallocate and clear up its “provisional” context.

[0349] Note 2: to simplify the logic, the ATCP driver will guaranteethat only one context may be in process of being handed out at a time:in other words, it will never issue another initial “intention” commanduntil it has completed the second half of the handshake for the firstone.

[0350] From INIC to ATCP.

[0351] There are two possible cases for this: a context transfer may beinitiated either by the ATCP driver or by the INIC. However themachinery will be very similar in the two cases. If the ATCP driverwishes to cause context to be flushed from INIC to host, it will send a“flus” message to the INIC specifying the context number to be flushed.Once the INIC receives this, it will proceed with the same steps as forthe case where the flush is initiated by the INIC itself:

[0352] 1) The INIC will send an error response to any currentoutstanding receive request it is working on (corresponding to an MDLinto which data is being placed.) Before sending the response, itupdates the receive command “length” field to reflect the amount of datawhich has actually been placed in the MDL buffers at the time of theflush.

[0353] 2) Likewise it will send an error response for any current sendrequest, again reporting the amount of data actually sent from therequest.

[0354] 3) The INIC will DMA the TCB for the context back to the host.(Note: part of the information provided with a context must be theaddress of the TCB in the host.)

[0355] 4) The INIC will send a “flush” indication to the host (verypreferably via the regular input path as a special type of frame)identifying the context which is being flushed. Sending this indicationvia the regular input path ensures that it will arrive before anyfollowing slow-path frames.

[0356] At this point, the INIC is no longer doing fast-path processing,and any further incoming frames for the connection will simply be sentto the host as raw frames for the slow input path. The ATCP driver maynot be able to complete the cleanup operations needed to resume normalslow path processing immediately on receipt of the “flush frame”, sincethere may be outstanding send and receive requests to which it has notyet received a response. If this is the case, the ATCP driver must set a“pend incoming TCP frames” flag in its per-connection context. Theeffect of this is to change the behavior of tcp_input( ). This runs as afunction call in the context of ip_input( ), and normally returns onlywhen incoming frames have been processed as far as possible (queued onthe socket receive buffer or out-of-sequence reassembly queue.) However,if there is a flush pending and we have not yet completedresynchronization, we cannot do TCP processing and must instead queueinput frames for TCP on a “holding queue” for the connection, to bepicked up later when context flush is complete and normal slow pathprocessing resumes. (This is why we want to send the “flush” indicationvia the normal input path: so that we can ensure it is seen before anyfollowing frames of slow-path input.)

[0357] Next we need to wait for any outstanding “send” requests to beerrored off:

[0358] 1) The INIC maintains its context for the connection in a“zombie” state. As “send” requests for this connection come out of theINIC queue, it sends error responses for them back to the ATCP driver.(It is apparently difficult for the INIC to identify all commandrequests for a given context; simpler for it to just continue processingthem in order, detecting ones that are for a “zombie” context as theyappear.)

[0359] 2) The ATCP driver has a count of the number of outstandingrequests it has sent to the INIC. As error responses for these arereceived, it decrements this count, and when it reaches zero, the ATCPdriver sends a “flush complete” message to the INIC.

[0360] 3) When the INIC receives the “flush complete” message, itdismantles its “zombie” context. From the INIC perspective, the flush isnow completed.

[0361] 4) When the ATCP driver has received error responses for alloutstanding requests, it has all the information needed to complete itscleanup. This involves completing any IRPs corresponding to requestswhich have entirely completed and adjusting fields inpartially-completed requests so that send and receive of slow path datawill resume at the right point in the byte streams.

[0362] 5) Once all this cleanup is complete, the ATCP driver will looppulling any “pended” TCP input frames off the “pending queue” mentionedabove and feeding them into the normal TCP input processing. Once allinput frames on this queue have been cleared off, the “pend incoming TCPframes” flag can be cleared for the connection, and we are back tonormal slow-path processing.

[0363] FreeBSD Porting Specification.

[0364] The largest portion of the ATCP driver is either derived, ordirectly taken from the FreeBSD TCP/IP protocol stack. This sectiondefines the issues associated with porting this code, the FreeBSD codeitself, and the modifications required for it to suit our needs.

[0365] Porting Philosophy.

[0366] FreeBSD TCP/IP (current version referred to as Net/3) is ageneral purpose TCP/IP driver. It contains code to handle a variety ofinterface types and many different kinds of protocols. To meet thisrequirement the code is often written in a sometimes confusing,over-complex manner. General-purpose structures are overlaid with otherinterface-specific structures so that different interface types cancoexist using the same general-purpose code. For our purposes much ofthis complexity is unnecessary since we are only supporting a singleinterface type and a few specific protocols. It is therefore tempting tomodify the code and data structures in an effort to make it morereadable, and perhaps a bit more efficient. There are, however, someproblems with doing this. First, the more we modify the originalFreeBSD, the more changes we will have to make. This is especially truewith regard to data structures. If we collapse two data structures intoone we might improve the cleanliness of the code a bit, but we will thenhave to modify every reference to that data structure in the entireprotocol stack. Another problem with attempting to “clean up” the codeis that we might later discover that we need something that we hadpreviously thrown away. Finally, while we might gain a small performanceadvantage in cleaning up the FreeBSD code, the FreeBSD TCP code willmostly only run in the slow-path connections, which are not our primaryfocus. Our priority is to get the slow-path code functional and reliableas quickly as possible.

[0367] For the reasons above we have adopted the philosophy that weshould initially keep the data structures and code at close to theoriginal FreeBSD implementation as possible. The code will be modifiedfor the following reasons:

[0368] 1) As required for NT interaction—Obviously we can't expect tosimply “drop-in” the FreeBSD code as is. The interface of this code tothe NT system will require some significant code modifications. Thiswill mostly occur at the topmost and bottommost portions of the protocolstack, as well as the “ioctl” sections of the code. Modifications forSMP issues are also needed.

[0369] 2) Unnecessary code can be removed—While we will keep the code asclose to the original FreeBSD as possible, we will nonetheless removecode that will never be used (UDP is a good example of this).

[0370] UNIX

NT Conversion.

[0371] The FreeBSD TCP/IP protocol stack makes use of many Unix systemservices. These include bcopy to copy memory, malloc to allocate memory,timestamp functions, etc. These will not be itemized in detail since theconversion to the corresponding NT calls is a fairly trivial andmechanical operation.

[0372] An area which will need non-trivial support redesign is MBUFs.

[0373] Network Buffers.

[0374] Under FreeBSD, network buffers are mapped using mbufs. Under NTnetwork buffers are mapped using a combination of packet descriptors andbuffer descriptors (the buffer descriptors are really MDLs). There are acouple of problems with the Microsoft method. First it does not providethe necessary fields which allow us to easily strip off protocolheaders. Second, converting all of the FreeBSD protocol code to speak interms of buffer descriptors is an unnecessary amount of overhead.Instead, in our port we will allocate our own mbuf structures and remapthe NT packets as shown in FIG. 29.

[0375] The mbuf structure will provide the standard fields provided inthe FreeBSD mbuf including the data pointer, which points to the currentlocation of the data, data length fields and flags. In addition eachmbuf will point to the packet descriptor which is associated with thedata being mapped. Once an NT packet is mapped, our transport drivershould never have to refer to the packet or buffer descriptors for anyinformation except when we are finished and are preparing to return thepacket.

[0376] There are a couple of things to note here. We have designed ourINIC such that a packet header should never be split across multiplebuffers. Thus, we should never require the equivalent of the “m_pullup”routine included in Unix. Also note that there are circumstances inwhich we will be accepting data that will also be accepted by theMicrosoft TCP/IP. One such example of this is ARP frames. We will needto build our own ARP cache by looking at ARP replies as they come offthe network. Under these circumstances, it is absolutely imperative thatwe do not modify the data, or the packet and buffer descriptors. We willdiscuss this further in the following sections.

[0377] We will allocate a pool of mbuf headers at ATCP initializationtime. It is important to remember that unlike other NICs, we can notsimply drop data if we run out of the system resources required tomanage/map the data. The reason for this is that we will be receivingdata from the card that has already been acknowledged by TCP. Because ofthis it is essential that we never run out of mbuf headers. To solvethis problem we will statically allocate mbuf headers for the maximumnumber of buffers that we will ever allow to be outstanding. By doingso, the card will run out of buffers in which to put the data before wewill run out of mbufs, and as a result, the card will be forced to dropdata at the link layer instead of us dropping it at the transport layer.DhXXX: as we've discussed, I don't think this is really true anymore.The INIC won't ACK data until either it's gotten a window update fromATCP to tell it the data's been accepted, or it's got an MDL. Thus itseems workable, though undesirable, if we can't accept a frame from theINIC & return an error to it saying it was not taken.

[0378] We will also require a pool of actual mbufs (not just headers).These mbufs are required in order to build transmit protocol headers forthe slow-path data path, as well as other miscellaneous purposes such asfor building ARP requests. We will allocate a pool of these atinitialization time and we will add to this pool dynamically as needed.Unlike the mbuf headers described above, which will be used to mapacknowledged TCP data coming from the card, the full mbufs will containdata that can be dropped if we can not get an mbuf.

[0379] The Code.

[0380] In this section we describe each section of the FreeBSD TCP/IPport. These sections include Interface Initialization, ARP, Route, IP,ICMP, and TCP.

[0381] Interface Initialization.

[0382] Structures.

[0383] There are a variety of structures, which represent a singleinterface in FreeBSD. These structures include: ifnet, arpeom, ifaddr,in ifaddr, sockaddr, sockaddr_in, and sockaddr_dl. FIG. 30 shows therelationship between all of these structures:

[0384] In the example of FIG. 30 we show a single interface with a MACaddress of 00:60:97:DB:9B:A6 configured with an IP address of192.100.1.2. As illustrated above, the in_faddr is actually an ifaddrstructure with some extra fields tacked on to the end. Thus the ifaddrstructure is used to represent both a MAC address and an IP address.Similarly the sockaddr structure is recast as a sockaddr_dl or asockaddr_in depending on its address type. An interface can beconfigured to multiple IP addresses by simply chaining in_ifaddrstructures after the in_ifaddr structure shown in FIG. 30.

[0385] As mentioned in the Porting Philosophy section, many of the abovestructures could likely be collapsed into fewer structures. In order toavoid making unnecessary modifications to FreeBSD, for the time being wewill leave these structures mostly as is. We will however eliminate thefields from the structure that will never be used. These structuremodifications are discussed below.

[0386] We also show above a structure called iface. This is a structurethat we define. It contains the arpcom structure, which in turn containsthe ifnet structure. It also contains fields that enable us to blend ourFreeBSD implementation with NT NDIS requirements. One such example isthe NDIS binding handle used to call down to NDIS with requests (such assend).

[0387] The Functions.

[0388] FreeBSD initializes the above structures in two phases. Firstwhen a network interface is found, the ifnet, arpcom, and first ifaddrstructures are initialized first by the network layer driver, and thenvia a call to the if_attach routine. The subsequent in_ifaddrstructure(s) are initialized when a user dynamically configures theinterface. This occurs in the in_ioctl and the in_ifinit routines. SinceNT allows dynamic configuration of a network interface we will continueto perform the interface initialization in two phases, but we willconsolidate these two phases as described below:

[0389] IFINIT.

[0390] The IfInit routine will be called from the ATKProtocolBindAdapterfunction. The IfInit function will initialize the Iface structure andassociated arpcom and ifnet structures. It will then allocate andinitialize an ifaddr structure in which to contain link-levelinformation about the interface, and a sockaddr_dl structure to containthe interface name and MAC address. Finally it will add a pointer to theifaddr structure into the ifnet_addrs array (using the if_index field ofthe ifnet structure) contained in the extended device object. IfInitwill then call IfConfig for each IP address that it finds in theregistry entry for the interface.

[0391] IFCONFIG.

[0392] IfConfig is called to configure an IP address for a giveninterface. It is passed a pointer to the ifnet structure for thatinterface along with all the information required to configure an IPaddress for that interface (such as IP address, netmask and broadcastinfo, etc). IfConfig will allocate an in_ifaddr structure to be used toconfigure the interface. It will chain it to the total chain ofin_ifaddr structures contained in the extended device object, and willthen configure the structure with the information given to it. Afterthat it will add a static route for the newly configured network andthen broadcast a gratuitous ARP request to notify others of our.Mac/IPaddress and to detect duplicate IP addresses on the net.

[0393] ARP.

[0394] We will port the FreeBSD ARP code to NT mostly as-is. For somereason, the FreeBSD ARP code is located in a file called if_ether.c.While the functionality of this file will remain the same, we willrename it to a more logical arp.c. The main structures used by ARP arethe 1linfo_arp structure and the rtentry structure (actually part ofroute). These structures will not require major modifications. Thefunctions that will require modification are defined here.

[0395] IN_ARPINPUT.

[0396] This function is called to process an incoming ARP frame. An ARPframe can either be an ARP request or an ARP reply. ARP requests arebroadcast, so we will see every ARP request on the network, while ARPreplies are directed so we should only see ARP replies that are sent tous. This introduces the following possible cases for an incoming ARPframe:

[0397] 1. ARP request trying to resolve our IP address—Under normalcircumstances, ARP would reply to this ARP request with an ARP replycontaining our MAC address. Since ARP requests will also be passed up tothe Microsoft TCP/IP driver, we need not reply. Note however, thatFreeBSD also creates or updates an ARP cache entry with the informationderived from the ARP request. It does this in anticipation of the factthat any host that wishes to know our MAC address is likely to wish totalk to us soon. Since we will need to know his MAC address in order totalk back, we might as well add the ARP information now rather thanissuing our own ARP request later.

[0398] 2. ARP request trying to resolve someone else's IP address—SinceARP requests are broadcast, we see every one on the network. When wereceive an ARP request of this type, we simply check to see if we havean entry for the host that sent the request in our ARP cache. If we do,we check to see if we still have the correct MAC address associated withthat host. If it is incorrect, we update our ARP cache entry. Note thatwe do not create a new ARP cache entry in this case.

[0399] 3. ARP reply—In this case we add the new ARP entry to our ARPcache. Having resolved the address, we check to see if there is anytransmit requests pending for the resolve IP address, and if so,transmit them.

[0400] Given the above three possibilities, the only major change to thein_arpinput code is that we will remove the code which generates an ARPreply for ARP requests that are meant for our interface.

[0401] ARPINTR.

[0402] This is the FreeBSD code that delivers an incoming ARP frame toin_arpinput. We will be calling in_arpinput directly from ourProtocolReceiveDPC routine (discussed in the NDIS section below) so thisfunction is not needed.

[0403] ARPWHOHAS.

[0404] This is a single line function that serves only as a wrapperaround arprequest. We will remove it and replace all calls to it withdirect calls to arprequest.

[0405] ARPREQUEST.

[0406] This code simply allocates a mbuf, fills it in with an ARPheader, and then passes it down to the ethernet output routine to betransmitted. For us, the code remains essentially the same except forthe obvious changes related to how we allocate a network buffer, and howwe send the filled in request.

[0407] ARP_IFINIT.

[0408] This is simply called when an interface is initialized tobroadcast a gratuitous ARP request (described in the interfaceinitialization section) and to set some ARP related fields in the ifaddrstructure for the interface. We will simply move this functionality intothe interface initialization code and remove this function.

[0409] ARPTIMER.

[0410] This is a timer-based function that is called every 5 minutes towalk through the ARP table looking for entries that have timed out.Although the time-out period for FreeBSD is 20 minutes, RFC 826 does notspecify any timer requirements with regard to ARP so we can modify thisvalue or delete the timer altogether to suit our needs. Either way thefunction won't require any major changes. All other functions inif_ether.c will not require any major changes.

[0411] Route.

[0412] On first thought, it might seem that we have no need for routingsupport since our ATCP driver will only receive IP datagrams whosedestination IP address matches that of one of our own interfaces.Therefore, we will not “route” from one interface to another. Instead,the MICROSOFT TCP/IP driver will provide that service. We will, however,need to maintain an up-to-date routing table so that we know a) whetheran outgoing connection belongs to one of our interfaces, b) to whichinterface it belongs, and c) what the first-hop IP address (gateway) isif the destination is not on the local network.

[0413] We discuss four aspects on the subject of routing in thissection. They are as follows:

[0414] 1. The mechanics of how routing information is stored.

[0415] 2. The manner in which routes are added or deleted from the routetable.

[0416] 3. When and how route information is retrieved from the routetable.

[0417] 4. Notification of route table changes to interested parties.

[0418] The Route Table.

[0419] In FreeBSD, the route table is maintained using an algorithmknown as PATRICIA (Practical Algorithm To Retrieve Information Coded inAlphanumeric). This is a complicated algorithm that is a bit costly toset up, but is very efficient to reference. Since the routing tableshould contain the same information for both NT and FreeBSD, and sincethe key used to search for an entry in the routing table will be thesame for each (the destination IP address), we should be able to portthe routing table software to NT without any major changes.

[0420] The software which implements the route table (via the PATRICIAalgorithm) is located in the FreeBSD file, radix.c. This file will beported directly to the ATCP driver with no significant changes required.

[0421] Adding and Deleting Routes.

[0422] Routes can be added or deleted in a number of different ways. Thekernel adds or deletes routes when the state of an interface changes orwhen an ICMP redirect is received. User space programs such as the RIPdaemon, or the route command also modify the route table.

[0423] For kernel-based route changes, the changes can be made by adirect call to the routing software. The FreeBSD software that isresponsible for the modification of route table entries is found inroute.c. The primary routine for all route table changes is calledrtrequest( ). It takes as its arguments, the request type (ADD, RESOLVE,DELETE), the destination IP address for the route, the gateway for theroute, the netmask for the route, the flags for the route, and a pointerto the route structure (struct rtentry) in which we will place the addedor resolved route. Other routines in the route.c file include rtinit( ),which is called during interface initialization time to add a staticroute to the network, rtredirect, which is called by ICMP when wereceive a ICMP redirect, and an assortment of support routines used forthe modification of route table entries. All of these routines found inroute.c will be ported with no major modifications.

[0424] For user-space-based changes, we will have to be a bit moreclever. In FreeBSD, route changes are sent down to the kernel fromuser-space applications via a special route socket. This code is foundin the FreeBSD file, rtsock.c. Obviously this will not work for our ATCPdriver. Instead the filter driver portion of our driver will interceptroute changes destined for the Microsoft TCP driver and will apply thosemodifications to our own route table via the rtrequest routine describedabove. In order to do this, it will have to do some format translationto put the data into the format (sockaddr_in) expected by the rtrequestroutine. Obviously, none of the code from rtsock.c will be ported to theATCP driver. This same procedure will be used to intercept and processexplicit ARP cache modifications.

[0425] Consulting the Route Table.

[0426] In FreeBSD, the route table is consulted in ip_output when an IPdatagram is being sent. In order to avoid a complete route table searchfor every outgoing datagram, the route is stored into the in_pcb for theconnection. For subsequent calls to ip_output, the route entry is thensimply checked to ensure validity. While we will keep this basicoperation as is, we will require a slight modification to allow us tocoexist with the Microsoft TCP driver. When an active connection isbeing set up, our filter driver will have to determine whether theconnection is going to be handled by one of the INIC interfaces. To dothis, we will have to consult the route table from the filter driverportion of our driver. This is done via a call to the rtallocl function(found in route.c). If a valid route table entry is found, then we willtake control of the connection and set a pointer to the rtentrystructure returned by rtallocl in our in_pcb structure.

[0427] What to do when a Route Changes.

[0428] When a route table entry changes, there may be connections thathave pointers to a stale route table entry. These connections will needto be notified of the new route. FreeBSD solves this by checking thevalidity of a route entry during every call to ip output. If the entryis no longer valid, its reference to the stale route table entry isremoved, and an attempt is made to allocate a new route to thedestination. For our slow path, this will work fine. Unfortunately,since our IP processing is handled by the INIC for our fast path, thissanity check method will not be sufficient. Instead, we will need toperform a review of all of our fast path connections during every routetable modification. If the route table change affects our connection, wewill need to advise the INIC with a new first-hop address, or if thedestination is no longer reachable, close the connection entirely.

[0429] ICMP.

[0430] Like the ARP code above, we will need to process certain types ofincoming ICMP frames. Of the 10 possible ICMP message types, there areonly three that we need to support. These include ICMP_REDIRECT,ICMP_UNREACH, and ICMP_SOURCEQUENCH. Any FreeBSD code to deal with othertypes of ICMP traffic will be removed. Instead, we will simply returnNDIS_STATUS_NOT_ACCEPTED for all but the above ICMP frame types. Thissection describes how we will handle these ICMP frames.

[0431] ICMP_REDIRECT.

[0432] Under FreeBSD, an ICMP_REDIRECT causes two things to occur.First, it causes the route table to be updated with the route given inthe redirect. Second, it results in a call back to TCP to cause TCP toflush the route entry attached to its associated in_pcb structures. Bydoing this, it forces ip_output to search for a new route. As mentionedin the Route section above, we will also require a call to a routinewhich will review all of the TCP fast-path connections, and update theroute entries as needed (in this case because the route entry has beenzeroed). The INIC will then be notified of the route changes.

[0433] ICMP_UNREACH.

[0434] In both FreeBSD and Microsoft TCP, the ICMP_UNREACH results in nomore than a simple statistic update. We will do the same.

[0435] ICMP_SOURCEQUENCH.

[0436] A source quench is sent to cause a TCP sender to close itscongestion window to a single segment, thereby putting the sender intoslow-start mode. We will keep the FreeBSD code as-is for slow-pathconnections. For fast path connections we will send a notification tothe card that the congestion window for the given connection has beenreduced. The INIC will then be responsible for the slow-start algorithm.

[0437] IP.

[0438] The FreeBSD IP code should require few modifications when portingto the ATCP driver. What few modifications will be required will bediscussed in this section.

[0439] IP Initialization.

[0440] During initialization time, ip_init is called to initialize thearray of protosw structures. These structures contain all theinformation needed by IP to be able to pass incoming data to the correctprotocol above it. For example, when a UDP datagram arrives, IP locatesthe protosw entry corresponding to the UDP protocol type value (0×11)and calls the input routine specified in that protosw entry. We willkeep the array of protosw structures intact, but since we are onlyhandling the TCP and ICMP protocols above IP, we will strip the protoswarray down substantially.

[0441] IP Input.

[0442] Following are the changes required for IP input (function ipintr( )).

[0443] No IP Forwarding.

[0444] Since we will only be handling datagrams for which we are thefinal destination, we should never be required to forward an IPdatagram. All references to IP forwarding, and the ip_forward functionitself, can be removed.

[0445] IP Options.

[0446] The only options supported by FreeBSD at this time include recordroute, strict and loose source and record route, and timestamp. For thetimestamp option, FreeBSD only logs the current time into the IP headerso that before it is forwarded. Since we will not be forwarding IPdatagrams, this seems to be of little use to us. While FreeBSD supportsthe remaining options, NT essentially does nothing useful with them. Forthe moment, we will not bother dealing with IP options. They will beadded in later if needed.

[0447] IP Reassembly.

[0448] There is a small problem with the FreeBSD IP reassembly code. Thereassembly code reuses the IP header portion of the IP datagram tocontain IP reassembly queue information. It can do this because it nolonger requires the original IP header. This is an absolute no-no withthe NDIS 4.0 method of handling network packets. The NT DDK explicitlystates that we must not modify packets given to us by NDIS. This is notthe only place in which the FreeBSD code modifies the contents of anetwork buffer. It also does this when performing endian conversions. Atthe moment we will leave this code as is and violate the DDK rules. Webelieve we can do this because we are going to ensure that no othertransport driver looks at these frames. If this becomes a problem wewill have to modify this code substantially by moving the IP reassemblyfields into the mbuf header.

[0449] IP Output.

[0450] There are only two modifications required for IP output. Thefirst is that since, for the moment, we are not dealing with IP options,there is no need for the code that inserts the IP options into the IPheader. Second, we may discover that it is impossible for us to everreceive an output request that requires fragmentation. Since TCPperforms Maximum Segment Size negotiation, we should theoretically neverattempt to send a TCP segment larger than the MTU.

[0451] NDIS Protocol Driver.

[0452] This section defines protocol driver portion of the ATCP driver.The protocol driver portion of the ATCP driver is defined by the set ofroutines registered with NDIS via a call to NdisRegisterProtocol. Theseroutines are limited to those that are called (indirectly) by the INICminiport driver beneath us. For example, we register aProtocolReceivePacket routine so that when the INIC driver callsNdisMIndicateReceivePacket it will result in a call from NDIS to ourdriver. Strictly speaking, the protocol driver portion of our driverdoes not include the method by which our driver calls down to theminiport (for example, the method by which we send network packets).Nevertheless, we will describe that method here for lack of a betterplace to put it. That said, we cover the following topics in thissection of the document: 1) Initialization; 2) Receive; 3) Transmit; 4)Query/Set Information; 5) Status indications; 6) Reset; and 7) Halt.

[0453] Initialization.

[0454] The protocol driver initialization occurs in two phases. Thefirst phase occurs when the ATCP DriverEntry routine callsATKProtoSetup. The ATKProtoSetup routine performs the following:

[0455] 1. Allocate resources—We attempt to allocate many of the requiredresources as soon as possible so that we are more likely to get thememory we want. This mostly applies to allocating and initializing ourmbuf and mbuf header pools.

[0456] 2. Register Protocol—We call NdisRegisterProtocol to register ourset of protocol driver routines.

[0457] 3. Locate and initialize bound NICs—We read the Linkageparameters of the registry to determine which NIC devices we are boundto. For each of these devices we allocate and initialize a IFACEstructure (defined above). We then read the TCP parameters out of theregistry for each bound device and set the corresponding fields in theIFACE structure.

[0458] After the underlying INIC devices have completed theirinitialization, NDIS will call our driver's ATKBindAdapter function foreach underlying device. It will perform the following:

[0459] 1. Open the device specified in the call the ATKBindAdapter.

[0460] 2. Find the IFACE structure that was created in ATKProtoSetup forthis device.

[0461] 3. Query the miniport for adapter information. This includes suchthings as link speed and MAC address. Save relevant information in theIFACE structure.

[0462] 4. Perform the interface initialization as specified in thesection on Interface Initialization.

[0463] Receive.

[0464] Receive is handled by the protocol driver routineATKReceivePacket. Before we describe this routine, it is important toconsider each possible receive type and how it will be handled.

[0465] Receive Overview.

[0466] Our INIC miniport driver will be bound to our transport driver aswell as the generic Microsoft TCP driver (and possibly others). The ATCPdriver will be bound exclusively to INIC devices, while the MicrosoftTCP driver will be bound to INIC devices as well as other types of NICs.This is illustrated in FIG. 31. By binding the driver in this fashion,we can choose to direct incoming network data to our own ATCP transportdriver, the Microsoft TCP driver, or both. We do this by playing withthe ethernet “type” field as follows.

[0467] To NDIS and the transport drivers above it, our card is going tobe registered as a normal ethernet card. When a transport driverreceives a packet from our driver, it will expect the data to start withan ethernet header, and consequently, expects the protocol type field tobe in byte offset 12. If Microsoft TCP finds that the protocol typefield is not equal to either IP, or ARP, it will not accept the packet.So, to deliver an incoming packet to our driver, we must simply map thedata such that byte 12 contains a non-recognized ethernet type field.Note that we must choose a value that is greater than 1500 bytes so thatthe transport drivers do not confuse it with an 802.3 frame. We mustalso choose a value that will not be accepted by other transport driversuch as Appletalk or IPX. Similarly, if we want to direct the data toMicrosoft TCP, we can then simply leave the ethernet type field set toIP (or ARP). Note that since we will also see these frames we can chooseto accept or not-accept them as necessary. Incoming packets aredelivered as follows:

[0468] A. Packets delivered to ATCP only (not accepted by MSTCP):

[0469] 1. All TCP packets destined for one of our IP addresses. Thisincludes both slow-path frames and fast-path frames. In the slow-pathcase, the TCP frames are given in there entirety (headers included). Inthe fast-path case, the ATKReceivePacket is given a header buffer thatcontains status information and data with no headers (except those aboveTCP). More on this later.

[0470] B. Packets delivered to Microsoft TCP only (not accepted byATCP):

[0471] 1. All non-TCP packets.

[0472] 2. All packets that are not destined for one of our interfaces(packets that will be routed). Continuing the above example, if there isan IP address 144.48.252.4 associated with the 3com interface, and wereceive a TCP connect with a destination IP address of 144.48.252.4, wewill actually want to send that request up to the ATCP driver so that wecreate a fast-path connection for it. This means that we will need toknow every IP address in the system and filter frames based on thedestination IP address in a given TCP datagram. This can be done in theINIC miniport driver. Since it will be the ATCP driver that learns ofdynamic IP address changes in the system, we will need a method tonotify the INIC miniport of all the IP addresses in the system. More onthis later.

[0473] C. Packets delivered to both:

[0474] 1. All ARP frames.

[0475] 2. All ICMP frames.

[0476] Two Types of Receive Packets.

[0477] There are several circumstances in which the INIC will need toindicate extra information about a receive packet to the ATCP driver.One such example is a fast path receive in which the ATCP driver willneed to be notified of how much data the card has buffered. Toaccomplish this, the first (and sometimes only) buffer in a receivedpacket will actually be an INIC header buffer. The header buffercontains status information about the receive packet, and may or may notcontain network data as well. The ATCP driver will recognize a headerbuffer by mapping it to an ethernet frame and inspecting the type fieldfound in byte 12. We will indicate all TCP frames destined for us inthis fashion, while frames that are destined for both our driver and theMicrosoft TCP driver (ARP, ICMP) will be indicated without a headerbuffer. FIG. 32 shows an example of an incoming TCP packet. FIG. 33shows an example of an incoming ARP frame.

[0478] NDIS 4 Protocolreceivepacket Operation.

[0479] NDIS has been designed such that all packets indicated viaNdisMIndicateReceivePacket by an underlying miniport are delivered tothe ProtocolReceivePacket routine for all protocol drivers bound to it.These protocol drivers can choose to accept or not accept the data. Theycan either accept the data by copying the data out of the packetindicated to it, or alternatively they can keep the packet and return itlater via a call to NdisReturnPackets. By implementing it in thisfashion, NDIS allows more than one protocol driver to accept a givenpacket. For this reason, when a packet is delivered to a protocoldriver, the contents of the packet descriptor, buffer descriptors anddata must all be treated as read-only. At the moment, we intend toviolate this rule. We choose to violate this because much of the FreeBSDcode modifies the packet headers as it examines them (mostly for endianconversion purposes). Rather than modify all of the FreeBSD code, wewill instead ensure that no other transport driver accepts the data bymaking sure that the ethernet type field is unique to us (no one elsewill want it). Obviously this only works with data that is onlydelivered to our ATCP driver. For ARP and ICMP frames we will insteadcopy the data out of the packet into our own buffer and return thepacket to NDIS directly. While this is less efficient than keeping thedata and returning it later, ARP and ICMP traffic should be smallenough, and infrequent enough, that it doesn't matter.

[0480] The DDK specifies that when a protocol driver chooses to keep apacket, it should return a value of 1 (or more) to NDIS in itsProtocolReceivePacket routine. The packet is then later returned to NDISvia the call to NdisReturnPackets. This can only happen after theProtocolReceivePacket has returned control to NDIS. This requires thatthe call to NdisReturnPackets must occur in a different executioncontext. We can accomplish this by scheduling a DPC, scheduling a systemthread, or scheduling a kernel thread of our own. For brevity in thissection, we will assume it is a done through a DPC. In any case, we willrequire a queue of pending receive buffers on which to place and fetchreceive packets.

[0481] After a receive packet is dequeued by the DPC it is then eitherpassed to TCP directly for fast-path processing, or it is sent throughthe FreeBSD path for slow-path processing. Note that in the case ofslow-path processing, we may be working on data that needs to bereturned to NDIS (TCP data) or we may be working on our own copy of thedata (ARP and ICMP). When we finish with the data we will need to figureout whether or not to return the data to NDIS or not. This will be donevia fields in the mbuf header used to map the data. When the mfreemroutine is called to free a chain of mbufs, the fields in the mbuf willbe checked and, if required, the packet descriptor pointed to by thembuf will be returned to NDIS.

[0482] MBUF

Packet Mapping.

[0483] As noted in the section on mbufs above, we will map incoming datato mbufs so that our FreeBSD port requires fewer modifications.Depending on the type of data received, this mapping will appeardifferently. Here are some examples:

[0484] In FIG. 34A, we show incoming data for a TCP fast-pathconnection. In this example, the TCP data is fully contained in theheader buffer. The header buffer is mapped by the mbuf and sent upstreamfor fast-path TCP processing. In this case it is required that theheader buffer be mapped and sent upstream because the fast-path TCP codewill need information contained in the header buffer in order to performthe processing. When the mbuf in this example is freed, the mfreemroutine will determine that the mbuf maps a packet that is owned by NDISand will then free the mbuf header only and call NdisReturnPackets tofree the data.

[0485] In FIG. 34B, we show incoming data for a TCP slow-pathconnection. In this example the mbuf points to the start of the TCP datadirectly instead of the header buffer. Since this buffer will be sent upfor slow-path FreeBSD processing, we can not have the mbuf pointing to aheader buffer (FreeBSD would get awfully confused). Again, when mfreemis called to free the mbuf, it will discover the mapped packet, free thembuf header, and call NDIS to free the packet and return the underlyingbuffers. Note that even though we do not directly map the header bufferwith the mbuf we do not lose it because of the link from the packetdescriptor. Note also that we could alternatively have the INIC miniportdriver only pass us the TCP data buffer when it receives a slow-pathreceive. This would work fine except that we have determined that evenin the case of slow-path connections we are going to attempt to offersome assistance to the host TCP driver (most likely by checksumprocessing only). In this case there may be some special fields that weneed to pass up to the ATCP driver from the INIC driver. Leaving theheader buffer connected seems the most logical way to do this.

[0486] Finally, in FIG. 34C, we show a received ARP frame. Recall thatfor incoming ARP and ICMP frames we are going to copy the incoming dataout of the packet and return it directly to NDIS. In this case the mbufsimply points to our data, with no corresponding packet descriptor. Whenwe free this mbuf, mfreem will discover this and free not only the mbufheader, but the data as well.

[0487] Other Receive Packets.

[0488] We use this receive mechanism for other purposes besides thereception of network data. It is also used as a method of communicationbetween the ATCP driver and the INIC. One such example is a TCP contextflush from the INIC. When the INIC determines, for whatever reason, thatit can no longer manage a TCP connection, it must flush that connectionto the ATCP driver. It will do this by filling in a header buffer withappropriate status and delivering it to the INIC driver. The INIC driverwill in turn deliver it to the protocol driver which will treat itessentially like a fast-path TCP connection by mapping the header bufferwith an mbuf header and delivering it to TCP for fast-path processing.There are two advantages to communicating in this manner. First, it isalready an established path, so no extra coding or testing is required.Second, since a context flush comes in, in the same manner as receivedframes, it will prevent us from getting a slow-path frame before thecontext has been flushed.

[0489] Summary

[0490] Having covered all of the various types of receive data,following are the steps that are taken by the ATKProtocolReceivePacketroutine.

[0491] 1. Map incoming data to an ethernet frame and check the typefield;

[0492] 2. If the type field contains our custom INIC type then it shouldbe TCP;

[0493] 3. If the header buffer specifies a fast-path connection,allocate one or more mbufs headers to map the header and possibly databuffers. Set the packet descriptor field of the mbuf to point to thepacket descriptor, set the mbuf flags appropriately, queue the mbuf, andreturn 1;

[0494] 4. If the header buffer specifies a slow-path connection,allocate a single mbuf header to map the network data, set the mbuffields to map the packet, queue the mbuf and return 1. Note that wedesign the INIC such that we will never get a TCP segment split acrossmore than one buffer;

[0495] 5. If the type field of the frame indicates ARP or ICMP;

[0496] 6. Allocate a mbuf with a data buffer. Copy the contents of thepacket into the mbuf. Queue the mbuf, and return 0 (not accepted); and

[0497] 7. If the type field is not either the INIC type, ARP or ICMP, wedon't want it. Return 0.

[0498] The receive processing will continue when the mbufs are dequeued.At the moment this is done by a routine called ATKProtocolReceiveDPC. Itwill do the following:

[0499] 1. Dequeue a mbuf from the queue; and

[0500] 2. Inspect the mbuf flags. If the mbuf is meant for fast-pathTCP, it will call the fast-path routine directly. Otherwise it will callthe ethernet input routine for slow-path processing.

[0501] Transmit.

[0502] In this section we discuss the ATCP transmit path.

[0503] NDIS 4 Send Operation.

[0504] The NDIS 4 send operation works as follows. When atransport/protocol driver wishes to send one or more packets down to anNDIS 4 miniport driver, it calls NdisSendPackets with an array of packetdescriptors to send. As soon as this routine is called, thetransport/protocol driver relinquishes ownership of the packets untilthey are returned, one by one in any order, via a NDIS call to theProtocolSendComplete routine. Since this routine is calledasynchronously, our ATCP driver must save any required context into thepacket descriptor header so that the appropriate resources can be freed.This is discussed further in the following sections.

[0505] Types of “Sends”.

[0506] Like the Receive path described above, the transmit path is usednot only to send network data, but is also used as a communicationmechanism between the host and the INIC. Here are some examples of thetypes of sends performed by the ATCP driver.

[0507] Fast-Path TCP Send.

[0508] When the ATCP driver receives a transmit request with anassociated MDL, it will package up the MDL physical addresses into acommand buffer, map the command buffer with a buffer and packetdescriptor, and call NdisSendPackets with the corresponding packet. Theunderlying INIC driver will issue the command buffer to the INIC. Whenthe corresponding response buffer is given back to the host, the INICminiport will call NdisMSendComplete which will result in a call to theATCP ProtocolSendComplete (ATKSendComplete) routine, at which point theresources associated with the send can be freed. We will allocate anduse a mbuf to hold the command buffer. By doing this we can store thecontext necessary in order to clean up after the send completes. Thiscontext includes a pointer to the MDL and presumably some otherconnection context as well. The other advantage to using a mbuf to holdthe command buffer is that it eliminates having another special set ofcode to allocate and return command buffer. We will store a pointer tothe mbuf in the reserved section of the packet descriptor so we canlocate it when the send is complete. FIG. 35 illustrates therelationship between the client's MDL, the command buffer, and thebuffer and packet descriptors.

[0509] Fast-Path TCP Receive.

[0510] As described in the Fast-Path Input Data Flow section above, thereceive process typically occurs in two phases. First the INIC fills ina host receive buffer with a relatively small amount of data, butnotifies the host of a large amount of pending data (either through alarge amount of buffered data on the card, or through a large amount ofexpected NetBios data). This small amount of data is delivered to theclient through the TDI interface. The client will then respond with aMDL in which the data should be placed. Like the Fast-path TCP sendprocess, the receive portion of the ATCP driver will then fill in acommand buffer with the MDL information from the client, map the bufferwith packet and buffer descriptors and send it to the INIC via a call toNdisSendPackets. Again, when the response buffer is returned to the INICminiport, the ATKSendComplete routine will be called and the receivewill complete. This relationship between the MDL, command buffer andbuffer and packet descriptors are the same as shown in the Fast-pathsend section above.

[0511] Slow-Path (FreeBSD).

[0512] Slow-path sends pass through the FreeBSD stack until the ethernetheader is prepended in ether_output and the packet is ready to be sent.At this point a command buffer will be filled with pointers to theethernet frame, the command buffer will be mapped with a packet andbuffer descriptor and NdisSendPackets will be called to hand the packetoff to the miniport. FIG. 36 shows the relationship between the mbufs,command buffer, and buffer and packet descriptors. Since we will use ambuf to map the command buffer, we can simply link the data mbufsdirectly off of the command buffer mbuf. This will make the freeing ofresources much simpler.

[0513] Non-Data Command Buffer.

[0514] The transmit path is also used to send non-data commands to thecard. As shown in FIG. 37, for example, the ATCP driver gives a contextto the INIC by filling in a command buffer, mapping it with a packet andbuffer descriptor, and calling NdisSendPackets.

[0515] ATKPROTOCOLSENDCOMPLETE.

[0516] Given the above different types of sends, theATKProtocolSendComplete routine will perform various types of actionswhen it is called from NDIS. First it must examine the reserved area ofthe packet descriptor to determine what type of request has completed.In the case of a slow-path completion, it can simply free the mbufs,command buffer, and descriptors and return. In the case of a fast-pathcompletion, it will need to notify the TCP fast path routines of thecompletion so TCP can in turn complete the client's IRP. Similarly, whena non-data command buffer completes, TCP will again be notified that thecommand sent to the INIC has completed.

[0517] TDI Filter Driver.

[0518] In a first embodiment of the product, the INIC handles onlysimple-case data transfer operations on a TCP connection. (These ofcourse constitute the large majority of CPU cycles consumed by TCPprocessing in a conventional driver.) There are many other complexitiesof the TCP protocol which must still be handled by host driver software:connection setup and breakdown, out-of-order data, nonstandard flags,etc.

[0519] The NT OS contains a fully functional TCP/IP driver, and onesolution would be to enhance this so that it is able to detect our INICand take advantage of it by “handing off” data-path processing whereappropriate.

[0520] Unfortunately, we do not have access to NT source, let alonepermission to modify NT. Thus the solution above, while a goal, cannotbe done immediately. We instead provide our own custom driver softwareon the host for those parts of TCP processing which are not handled bythe INIC.

[0521] This presents a challenge. The NT network driver framework doesmake provision for multiple types of protocol driver: but it does noteasily allow for multiple instances of drivers handling the SAMEprotocol.

[0522] For example, there are no “hooks” into the Microsoft TCP/IPdriver which would allow for routing of IP packets between our driver(handling our INICs) and the Microsoft driver (handling other NICs).

[0523] Our approach to this is to retain the Microsoft driver for allnon-TCP network processing (even for traffic on our INICs), but toinvisibly “steal” TCP traffic on our connections and handle it via ourown (BSD-derived) driver. The Microsoft TCP/IP driver is unaware of TCPconnections on interfaces we handle.

[0524] The network “bottom end” of this artifice is described earlier inthe document. In this section we will discuss the “top end”: the TDIinterface to higher-level NT network client software.

[0525] We make use of an NT facility called a filter driver. NT allows aspecial type of driver (“filter driver”) to attach itself “on top” ofanother driver in the system. The NT I/O manager then arranges that allrequests directed to the attached driver are sent first to the filterdriver; this arrangement is invisible to the rest of the system.

[0526] The filter driver may then either handle these requests itself,or pass them down to the underlying driver it is attached to. Providedthe filter driver completely replicates the (externally visible)behavior of the underlying driver when it handles requests itself, theexistence of the filter driver is invisible to higher-level software.

[0527] The filter driver attaches itself on top of the Microsoft TCP/IPdriver; this gives us the basic mechanism whereby we can interceptrequests for TCP operations and handle them in our driver instead of theMicrosoft driver.

[0528] However, while the filter driver concept gives us a framework forwhat we want to achieve, there are some significant technical problemsto be solved. The basic issue is that setting up a TCP connectioninvolves a sequence of several requests from higher-level software, andit is not always possible to tell, for requests early in this sequence,whether the connection should be handled by our driver or by theMicrosoft driver.

[0529] Thus for many requests, we store information about the request incase we need it later, but also allow the request to be passed down tothe Microsoft TCP/IP driver in case the connection ultimately turns outto be one which that driver should handle.

[0530] Let us look at this in more detail, which will involve someexamination of the TDI interface: the NT interface into the top end ofNT network protocol drivers. Higher-level TDI client software whichrequires services from a protocol driver proceeds by creating varioustypes of NT FILE_OBJECTs, and then making various DEVICE_IO_CONTROLrequests on these FILE_OBJECTs.

[0531] There are two types of FILE_OBJECT of interest here. Local IPaddresses that are represented by ADDRESS objects, and TCP connectionsthat are represented by CONNECTION objects. The steps involved insetting up a TCP connection (from the “active” client side, for aCONNECTION object) are:

[0532] 1) Create an ADDRESS object; 2) Create a CONNECTION object; 3)Issue a TDI_ASSOCIATE_ADDRESS io-control to associate the CONNECTIONobject with the ADDRESS object; and 4) Issue a TDI_CONNECT io-control onthe CONNECTION object, specifying the remote address and port for theconnection.

[0533] Initial thoughts were that handling this would bestraightforward: we would tell, on the basis of the address given whencreating the ADDRESS object, whether the connection is for one of ourinterfaces or not. After which, it would be easy to arrange for handlingentirely by our code, or entirely by the Microsoft code: we would simplyexamine the ADDRESS object to see if it was “one of ours” or not.

[0534] There are two main difficulties, however. First, when theCONNECTION object is created, no address is specified: it acquires alocal address only later when the TDI_ASSOCIATE_ADDRESS is done. Also,when a CONNECTION object is created, the caller supplies an opaque“context cookie” which will be needed for later communications with thatcaller. Storage of this cookie is the responsibility of the protocoldriver: it is not directly derivable just by examination of theCONNECTION object itself. If we simply passed the “create” call down tothe Microsoft TCP/IP driver, we would have no way of obtaining thiscookie later if it turns out that we need to handle the connection.Therefore, for every CONNECTION object which is created we allocate astructure to keep track of information about it, and store thisstructure in a hash table keyed by the address of the CONNECTION objectitself, so that we can locate it if we later need to process requests onthis object. We refer to this as a “shadow” object: it replicatesinformation about the object stored in the Microsoft driver. (We must,of course, also pass the create request down to the Microsoft drivertoo, to allow it to set up its own administrative information about theobject.)

[0535] A second major difficulty arises with ADDRESS objects. These areoften created with the TCP/IP “wildcard” address (all zeros); the actuallocal address is assigned only later during connection setup (by theprotocol driver itself.) Of course, a “wildcard” address does not allowus to determine whether connections that will be associated with thisADDRESS object should be handled by our driver or by the Microsoft one.Also, as with CONNECTION objects, there is “opaque” data associated withADDRESS objects that cannot be derived just from examination of theobject itself. (In this case addresses of callback functions set on theobject by TDI_SET_EVENT io-controls.)

[0536] Thus, as in the CONNECTION object case, we create a “shadow”object for each ADDRESS object which is created with a wildcard address.In this we store information (principally addresses of callbackfunctions) which we will need if we are handling connections onCONNECTION objects associated with this ADDRESS object. We store similarinformation, of course, for any ADDRESS object which is explicitly forone of our interface addresses; in this case we don't need to also passthe create request down to the Microsoft driver.

[0537] With this concept of “shadow” objects in place, let us revisitthe steps involved in setting up a connection, and look at theprocessing required in our driver.

[0538] First, the TDI client makes a call to create the ADDRESS object.Assuming that this is a “wildcard” address, we create a “shadow” objectbefore passing the call down to the Microsoft driver.

[0539] The next step (omitted in the earlier list for brevity) isnormally that the client makes a number of TDI_SET_EVENT io-controlcalls to associate various callback functions with the ADDRESS object.These are functions that should be called to notify the TDI client whencertain events (such arrival of data or disconnection requests etc)occur. We store these callback function pointers in our “shadow” addressobject, before passing the call down to the Microsoft driver.

[0540] Next, the TDI client makes a call to create a CONNECTION object.Again, we create our “shadow” of this object.

[0541] Next, the client issues the TDI_ASSOCIATE_ADDRESS io-control tobind the CONNECTION object to the ADDRESS object. We note theassociation in our “shadow” objects, and also pass the call down to theMicrosoft driver.

[0542] Finally the TDI client issues a TDI_CONNECT io-control on theCONNECTION object, specifying the remote IP address (and port) for thedesired connection. At this point, we examine our routing tables todetermine if this connection should be handled by one of our interfaces,or by some other NIC. If it is ours, we mark the CONNECTION object as“one of ours” for future reference (using an opaque field which NTFILE_OBJECTS provide for driver use.) We then proceed with connectionsetup and handling in our driver, using information stored in our“shadow” objects. The Microsoft driver does not see the connectionrequest or any subsequent traffic on the connection.

[0543] If the connection request is NOT for one of our interfaces, wepass it down to the Microsoft driver. Note carefully, however, that wecan not simply discard our “shadow” objects at this point. The TDIinterface allows re-use of CONNECTION objects: on termination of aconnection, it is legal for the TDI client to dissociate the CONNECTIONobject from its current . Thus our “shadow” objects must be retained forthe lifetime ADDRESS object, re-associate it with another, and use itfor another connection of the NT FILE_OBJECTS: the subsequent connectioncould turn out to be via one of our interfaces.

[0544] Timers.

[0545] Keepalive Timer.

[0546] We don't want to implement keepalive timers on the INIC. It wouldin any case be a very poor use of resources to have an INIC contextsitting idle for two hours.

[0547] Idle Timer.

[0548] We will keep an idle timer in the ATCP driver for connectionsthat are managed by the INIC (resetting it whenever we see activity onthe connection), and cause a flush of context back to the host if thistimer expires. We may want to make the threshold substantially lowerthan 2 hours, to reclaim INIC context slots for useful work sooner. Mayalso want to make that dependent on the number of contexts which haveactually been handed out: don't need to reclaim them if we haven'thanded out the max.

[0549] Receive and Transmit Microcode Design.

[0550] This section provides a general description of the design of themicrocode that will execute on two of the sequencers of the ProtocolProcessor on the INIC. The overall philosophy of the INIC is discussedin other sections. This section will discuss the INIC microcode indetail.

[0551] Design Overview.

[0552] As specified in other sections, the INIC supplies a set of 3custom processors that will provide considerable hardware-assist to themicrocode running thereon. The paragraphs immediately following list themain hardware-assist features:

[0553] 1) Header processing with specialized DMA engines to validate aninput header and generate a context hash, move the header into fastmemory and do header comparisons on a DRAM-based TCP control block;

[0554] 2) DRAM fifos for free buffer queues (large & small),receive-frame queues, event queues etc.;

[0555] 3) Header compare logic;

[0556] 4) Checksum generation;

[0557] 5) Multiple register contexts with register access controlled bysimply setting a context register. The Protocol Processor will provide512 SRAM-based registers to be shared among the 3 sequencers;

[0558] 6) Automatic movement of input frames into DRAM buffers from theMAC Fifos;

[0559] 7) Run receive processing on one sequencer and transmitprocessing on the other. This was chosen as opposed to letting bothsequencers run receive and transmit. One of the main reasons for this isthat the header-processing hardware can not be shared and interlockswould be needed to do this. Another reason is that interlocks would beneeded on the resources used exclusively by receive and by transmit;

[0560] 8) The INIC will support up to 256 TCP connections (TCB's). A TCBis associated with an input frame when the frame's source anddestination IP addresses and source and destination ports match that ofthe TCB. For speed of access, the TCB's will be maintained in a hashtable in NIC DRAM to save sequential searching. There will however, bean index in hash order in SRAM. Once a hash has been generated, the TCBwill be cached in SRAM. There will be up to 8 cached TCBs in SRAM. Thesecache locations can be shared between both sequencers so that thesequencer with the heavier load will be able to use more cache buffers.There will also be 8 header buffers to be shared between the sequencers.Note that each header buffer is not statically linked to a specific TCBbuffer. In fact the link is dynamic on a per-frame basis. The need forthis dynamic linking will be explained in later sections. Suffice to sayhere that if there is a free header buffer, then somewhere there is alsoa free TCB SRAM buffer;

[0561] 9) There were 2 basic implementation options considered here. Thefirst was single-stack and the second was a process model. The processmodel was chosen here because the custom processor design is providingzero-cost overhead for context switching through the use of a contextbase register, and because there will be more than enough process slots(or contexts) available for the peak load. It is also expected that all“local” variables will be held permanently in registers whilst an eventis being processed;

[0562] 10) The features that provide this are 256 of the 512 SRAM-basedregisters that will be used for the register contexts. This can bedivided up into 16 contexts (or processes) of 16 registers each. Then 8of these will be reserved for receive and 8 for transmit. A Little's Lawanalysis has shown that in order to support 512 byte frames at maximumarrival rate of 4*100 Mbits, requires more than 8 jobs to be in processin the NIC. However each job requires an SRAM buffer for a TCB contextand at present, there are only 8 of these currently specified due toSRAM space limits. So more contexts (e.g. 32*8 regs each) do not seemworthwhile. Refer to the section entitled “LOAD CALCULATIONS” for moredetails of this analysis. A context switch simply involves reloading thecontext base register based on the context to be restarted, and jumpingto the appropriate address for resumption;

[0563] 11) To better support the process model chosen, the code willlock an active TCB into an SRAM buffer while either sequencer isoperating on it. This implies there will be no swapping to and from DRAMof a TCB once it is in SRAM and an operation is started on it. Morespecifically, the TCB will not be swapped after requesting that a DMA beperformed for it. Instead, the system will switch to another active“process”. Then it will resume the former process at the point directlyafter where the DMA was requested. This constitutes a zero-cost switchas mentioned above;

[0564] 12) Individual TCB state machines will be run from within a“process”. There will be a state machine for the receive side and onefor the transmit side. The current TCB states will be stored in the SRAMTCB index table entry;

[0565] 13) The INIC will have 16 MB of DRAM. The current specificationcalls for dividing a large portion of this into 2 K buffers and controlallocation/deallocation of these buffers through one of the DRAM fifosmentioned above. These fifos will also be used to control small hostbuffers, large host buffers, command buffers and command responsebuffers;

[0566] 14) For events from one sequencer to the other (i.e. RCV

XMT), the current specification calls for using simple SRAM CIO buffers,one for each direction;

[0567] 15) Each sequencer handles its own timers independently of theothers;

[0568] 16) Contexts will be passed to the INIC through the Transmitcommand and response buffers. INIC-initiated TCB releases will behandled through the Receive small buffers. Host-initiated releases willuse the Command buffers. There needs to be strict handling of theacquisition and release of contexts to avoid windows where for example,a frame is received on a context just after the context was passed tothe INIC, but before the INIC has “accepted” it; and

[0569] 17) T/TCP (Transaction TCP): the initial INIC will not handleT/TCP connections. This is because they are typically used for the HTTPprotocol and the client for that protocol typically connects, sends arequest and disconnects in one segment. The server sends the connectconfirm, reply and disconnect in his first segment. Then the clientconfirms the disconnect. This is a total of 3 segments for the life of acontext. Typical data lengths are on the order of 300 bytes from theclient and 3 K from the server. The INIC will provide as good an assistas seems necessary here by checksumming the frame and splitting headersand data. The latter is only likely when data is forwarded with arequest such as when a filled-in form is sent by the client.

[0570] SRAM Requirements.

[0571] SRAM requirements for the Receive and Transmit engines are shownin FIG. 38. Depending upon the available space, the number of TCBbuffers may be increased to 16.

[0572] General Philosophy.

[0573] The basic plan is to have the host determine when a TCPconnection is able to be handed to the INIC, setup the TCB and pass itto the card via a command in the Transmit queue. TCBs that the INIC ownscan be handed back to the host via a request from the Receive orTransmit sequencers or from the host itself at any time.

[0574] When the INIC receives a frame, one of its immediate tasks is todetermine if the frame is for a TCB that it controls. If not, the frameis passed to the host on a generic interface TCB. On transmit, thetransmit request will specify a TCB hash number if the request is on aINIC-controlled TCB. Thus the initial state for the INIC will betransparent mode in which all received frames are directly passedthrough and all transmit requests will be simply thrown on theappropriate wire. This state is maintained until the host passes TCBs tothe INIC to control. Note that frames received for which the INIC has noTCB (or it is with the host) will still have the TCP checksum verifiedif TCP/IP, and may split the TCPIP header off into a separate buffer.

[0575] Register Usage.

[0576] There will be 512 registers available. The first 256 will be usedfor process contexts. The remaining 256 will be split between the threesequencers as follows: 1) 257-320: 64 for RCV general processing/mainloop; 2) 321-384: 64 for XMT general processing/main loop; and 3)385-512: 128 for three sequencer use.

[0577] Receive Processing.

[0578] Main Loop.

[0579]FIG. 39 is a summary of the main loop of Receive.

[0580] Receive Events.

[0581] The events that will be processed on a given context are:

[0582] 1) accept a context;

[0583] 2) release a context command (from the host via Transmit);

[0584] 3) release a context request (from Transmit);

[0585] 4) receive a valid frame; this will actually become 2 eventsbased on the received frame—receive an ACK, receive a segment;

[0586] 5) receive an “invalid” frame i.e. one that causes the TCB to beflushed to the host;

[0587] 6) a valid ACK needs to be sent (delayed ACK timer expiry); and

[0588] 7) There are expected to be the following sources of events: a)Receive input queue: it is expected that hardware will automatically DMAarriving frames into frame buffers and queue an event into a RCV-eventqueue; b) Timer event queue: expiration of a timer will queue an eventinto this queue; and c) Transmit sequencer queue: for requests from thetransmit processor.

[0589] For the sake of brevity the following only discussesreceive-frame processing.

[0590] Receive Details—Valid Context.

[0591] The base for the receive processing done by the INIC on anexisting context is the fast-path or “header prediction” code in theFreeBSD release. Thus the processing is divided into three parts: headervalidation and checksumming, TCP processing and subsequent SMBprocessing.

[0592] Header Validation.

[0593] There is considerable hardware assist here. The first step inreceive processing is to DMA the frame header into an SRAM headerbuffer. It is useful for header validation to be implemented inconjunction with this DMA by scanning the data as it flies by. Thefollowing tests need to be “passed”:

[0594] 1) MAC header: destination address is our MAC address (not MC orBC too), the Ethertype is IP; 2) IP header: header checksum is valid,header length=5, IP length>header length, protocol=TCP, nofragmentation, destination IP is our IP address; and 3) TCP header:checksum is valid (incl. pseudo-header), header length=5 or 8 (timestampoption), length is valid, dest port=SMB or FTP data, noFIN/SYN/URG/PSH/RST bits set, timestamp option is valid if present,segment is in sequence, the window size did not change, this is not aretransmission, it is a pure ACK or a pure receive segment, and mostimportant, a valid context exists. The valid-context test is non-trivialin the amount of work involved to determine it. Also note that for pureACKs, the window-size test will be relaxed. This is because initiallythe output PERSIST state is to be handled on the INIC.

[0595] Many but perhaps not all of these tests will be performed inhardware—depending upon the embodiment.

[0596] TCP Processing.

[0597] Once a frame has passed the header validation tests, processingsplits based on whether the frame is a pure ACK or a pure receivedsegment.

[0598] Pure RCV Packet.

[0599] The design is to split off headers into a small header buffer andpass the aligned data in separate large buffers. Since a frame has beenreceived, eventually some receiver process on the host will need to beinformed. In the case of FTP, the frame is pure data and it is passed tothe host immediately. This involves getting large buffers and DMAing thedata into them, then setting the appropriate details in a small bufferthat is used to notify the host. However for SMB, the INIC is performingreassembly of data when the frame consists of headers and data. So theremay not yet be a complete SMB to pass to the host. In this case, a smallbuffer will be acquired and the header moved into it. If the receivedsegment completes an SMB, then the procedures are pretty much as forFTP. If it does not, then the scheme is to at least move the receiveddata (not the headers) to the host to free the INIC buffers and to savelatency. The list of in-progress host buffers is maintained in the TCBand moved to the header buffer when the SMB is complete.

[0600] The final part of pure-receive processing is to fire off thedelayed ACK timer for this segment.

[0601] Pure ACK.

[0602] Pure ACK processing implies this TCB is the sender, so there maybe transmit buffers that can be returned to the host. If so, send anevent to the Transmit processor (or do the processing here). If there ismore output available, send an event to the transmit processor.

[0603] Then appropriate actions need to be taken with the retransmissiontimer.

[0604] SMB Processing.

[0605]FIG. 40 shows the format of the SMB header of an SMB frame. TheLENGTH field of the NetBIOS header will be used to determine when acomplete SMB has been received and the header buffer with appropriatedetails can be posted to the host. The interesting commands are thewrite commands: SMBwrite (0xB), SMBwriteBraw (0x1D), SMBwriteBmpx(0x1E), SMBwriteBs (0x1F), SMBwriteclose (0x2C), SMBwriteX (0x2F),SMBwriteunlock (0x14). These are interesting because they will have datato be aligned in host memory. The point to note about these commands isthat they each have a different WCT field, so that the start offset ofthe data depends on the command type. SMB processing will thus need tobe cognizant of these types.

[0606] Receive Details—No Valid Context.

[0607] The design here is to provide as much assist as possible. Frameswill be checksummed and the TCPIP headers may be split off.

[0608] Receive Notes.

[0609] 1. PRU_RCVD or the equivalent in Microsoft language: the hostapplication has to tell the INIC when he has accepted the received datathat has been queued. This is so that the INIC can update the receivewindow. It is an advantage for this mechanism to be efficient. This maybe accomplished by piggybacking these on transmit requests (notnecessarily for the same TCB).

[0610] 2. Keepalive Timer: for a INIC-controlled TCB, the INIC will notmaintain this timer. This leaves the host with the job of determiningthat the TCB is still active.

[0611] 3. Timestamp option: it is useful to support this option in thefast path because the BSD implementation does. Also, it can be veryhelpful in getting a much better estimate of the round-trip time (RTT)which TCP needs to use.

[0612] 4. Idle timer: the INIC will not maintain this timer (see Note 2above).

[0613] 5. Frame with no valid context: The INIC may split TCP/IP headersinto a separate header buffer.

[0614] Transmit Processing.

[0615] Main Loop.

[0616]FIG. 41 is a summary of the main loop of Transmit.

[0617] Transmit Events.

[0618] The events that will be processed on a given context and theirsources are: 1) accept a context (from the Host); 2) release a contextcommand (from the Host); 3) release a context command (from Receive); 4)valid send request and window>0 (from host or RCV sequencer); 5) validsend request and window=0 (from host or RCV sequencer); 6) send a windowupdate (host has accepted data); 7) persist timer expiration (persisttimer); 8) context-release event e.g. window shrank (XMT processing orretransmission timer); and 9) receive-release request ACK( from RCVsequencer).

[0619] Transmit Details—Valid Context.

[0620] The following is an overview of the transmit flow: The host postsa transmit request to the INIC by filling in a command buffer withappropriate data pointers etc and posting it to the INIC via the CommandBuffer Address register. Note that there is one host command bufferqueue, but there are four physical transmit lines. So each request needsto include an interface number as well as the context number. The INICmicrocode will DMA the command in and place it in one of four internalcommand queues which the transmit sequencer will work on. This is sothat transmit processing can round-robin service these four queues tokeep all four interfaces busy, and not let a highly-active interfacelock out the others (which would happen with a single queue). Thetransmit request may be a segment that is less than the MSS, or it maybe as much as a full 64 K SMB READ. Obviously the former request will goout as one segment, the latter as a number of MSS-sized segments. Thetransmitting TCB must hold on to the request until all data in it hasbeen transmitted and acked. Appropriate pointers to do this will be keptin the TCB. A large buffer is acquired from the free buffer fifo, andthe MAC and TCP/IP headers are created in it. It may be quicker/simplerto keep a basic frame header set up in the TCB and either DMA directlythis into the frame each time. Then data is DMA'd from host memory intothe frame to create an MSS-sized segment. This DMA also checksums thedata. Then the checksum is adjusted for the pseudo-header and placedinto the TCP header, and the frame is queued to the MAC transmitinterface which may be controlled by the third sequencer. The final stepis to update various window fields etc in the TCB. Eventually either theentire request will have been sent and acked, or a retransmission timerwill expire in which case the context is flushed to the host. In eithercase, the INIC will place a command response in the Response queuecontaining the command buffer handle from the original transmit commandand appropriate status.

[0621] The above discussion has dealt how an actual transmit occurs.However the real challenge in the transmit processor is to determinewhether it is appropriate to transmit at the time a transmit requestarrives. There are many reasons not to transmit: the receiver's windowsize is <=0, the Persist timer has expired, the amount to send is lessthan a full segment and an ACK is expected/outstanding, the receiver'swindow is not half-open etc. Much of the transmit processing will be indetermining these conditions.

[0622] Transmit Details—No Valid Context.

[0623] The main difference between this and a context-based transmit isthat the queued request here will already have the appropriate MAC andTCP/IP (or whatever) headers in the frame to be output. Also the requestis guaranteed not to be greater than MSS-sized in length. So theprocessing is fairly simple. A large buffer is acquired and the frame isDMAed into it, at which time the checksum is also calculated. If theframe is TCP/IP, the checksum will be appropriately adjusted ifnecessary (pseudo-header etc) and placed in the TCP header. The frame isthen queued to the appropriate MAC transmit interface. Then the commandis immediately responded to with appropriate status through the Responsequeue.

[0624] Transmit Notes.

[0625] 1) Slow-start: the INIC will handle the slow-start algorithm thatis now a part of the TCP standard. This obviates waiting until theconnection is sending a full-rate before passing it to the INIC.

[0626] 2) Window Probe vs Window Update—an explanation for posterity. AWindow Probe is sent from the sending TCB to the receiving TCB, and itmeans the sender has the receiver in PERSIST state. Persist state isentered when the receiver advertises a zero window. It is thus the stateof the transmitting TCB. In this state, he sends periodic window probesto the receiver in case an ACK from the receiver has been lost. Thereceiver will return his latest window size in the ACK. A Window Updateis sent from the receiving TCB to the sending TCB, usually to tell himthat the receiving window has altered. It is mostly triggered by theupper layer when it accepts some data. This probably means the sendingTCB is viewing the receiving TCB as being in PERSIST state.

[0627] 3) Persist state: it is designed to handle Persist state on theINIC. It seems unreasonable to throw a TCB back to the host just becauseits receiver advertised a zero window. This would normally be atransient situation, and would tend to happen mostly with clients thatdo not support slow-start. Alternatively, the code can easily be changedto throw the TCB back to the host as soon as a receiver advertises azero window.

[0628] 4) MSS-sized frames: the INIC code will expect all transmitrequests for which it has no TCB to not be greater than the MSS. If anyrequest is, it will be dropped and an appropriate response statusposted.

[0629] 5) Silly Window avoidance: as a receiver, the INIC will do theright thing here and not advertise small windows—this is easy. Howeverit is necessary to also do things to avoid this as a sender, for thecases where a stupid client does advertise small windows. Withoutgetting into too much detail here, the mechanism requires the INIC codeto calculate the largest window advertisement ever advertised by theother end. It is an attempt to guess the size of the other end's receivebuffer and assumes the other end never reduces the size of its receivebuffer. See Stevens, “TCP/IP Illustrated”, Vol. 1, pp. 325-326 (1994).

[0630] The Utility Processor.

[0631] Summary.

[0632] The following is a summary of the main functions of the utilitysequencer of the microprocessor:

[0633] 1) Look at the event queues: Event13Type & Event23Type (we assumethere will be an event status bit for this—USE_EV13 and USE_EV23) in theevents register; these are events from sequencers 1 and 2; they willmainly be XMIT requests from the XMT sequencer. Dequcue request andplace the frame on the appropriate interface.

[0634] 2) RCV-frame support: in the model, RCV is done throughVinicReceive( ) which is registered by the lower-edge driver, and iscalled at dispatch-level. This routine calls VinicTransferDataComplete() to check if the xfer (possibly DMA) of the frame into host buffers iscomplete. The latter rtne is also called at dispatch level on aDMA-completion interrupt. It queues complete buffers to the RCVsequencer via the normal queue mechanism.

[0635] 3) Other processes may also be employed here for supporting theRCV sequencer.

[0636] 4) Service the following registers (this will probably involvemicro-interrupts):

[0637] a) Header Buffer Address register:

[0638] Buffers are 256 bytes long on 256-byte boundaries.

[0639]31-8—physical addr in host of a set of contiguous hddr buffers.

[0640]7-0—number of hddr buffers passed.

[0641] Use contents to add to SmallHType queue.

[0642] b) Data Buffer Handle & Data Buffer Address registers:

[0643] Buffers are 4 K long aligned on 4 K boundaries.

[0644] Use contents to add to the FreeType queue.

[0645] c) Command Buffer Address register:

[0646] Buffers are multiple of 32 bytes up to 1 K long (2**5*32).

[0647]31-5—physical addr in host of cmd buffer.

[0648]4-0—length of cmd in bytes/32 (i.e. multiples of 32 bytes).

[0649] Points to host cmd; get FreeSType buffer and move.

[0650] command into it; queue to Xmit0-Xmit3Type queues.

[0651] d) Response Buffer Address register:

[0652] Buffers are 32 bytes long on 32-byte boundaries.

[0653]31-8—physical addr in host of a set of contiguous resp buffers.

[0654]7-0—number of resp buffers passed.

[0655] Use contents to add to the ResponseType queue.

[0656] 5) Low buffer threshold support: set approp bits in the ISR whenthe available-buffers count in the various queues filled by the hostfalls below a threshold.

[0657] Further Operations of the Utility Processor.

[0658] The utility processor of the microprocessor housed on the INIC isresponsible for setting up and implementing all configuration space andmemory mapped operations, and also as described below, for managing thedebug interface.

[0659] All data transfers, and other INIC initiated transfers will bedone via DMA. Configuration space for both the network processorfunction and the utility processor function will define a single memoryspace for each. This memory space will define the basic communicationstructure for the host. In general, writing to one of these memorylocations will perform a request for service from the INIC. This isdetailed in the memory description for each function. This sectiondefines much of the operation of the Host interface, but should be readin conjunction with the Host Interface Strategy for the Alacritech INICto fully define the Host/INIC interface.

[0660] Two registers, DMA hardware and an interrupt function comprisethe INIC interface to the Host through PCI. The interrupt function isimplemented via a four bit register (PCI_INT) tied to the PCI interruptlines. This register is directly accessed by the microprocessor.

[0661] THE MICROPROCESSOR uses two registers, the PCI_Data_Reg and thePCI_Address Reg, to enable the Host to access Configuration Space andthe memory space allocated to the INIC. These registers are notavailable to the Host, but are used by THE MICROPROCESSOR to enable Hostreads and writes. The function of these two registers is as follows.

[0662] 1) PCI_Data_Reg: This register can be both read and written byTHE MICROPROCESSOR. On write operations from the host, this registercontains the data being sent from the host. On read operations, thisregister contains the data to be sent to the host.

[0663] 2) PCI_Address Reg: This is the control register for memory readsand writes from the host. The structure of the register is shown in FIG.42. During a write operation from the Host the PCI_Data_Reg containsvalid data after Data Valid is set in the PCI_Address_Reg. Bothregisters are locked until THE MICROPROCESSOR writes the PCI_Data_Reg,which resets Data Valid. All read operations will be direct from SRAM.Memory space based reads will return 00. Configuration space reads willbe mapped as shown in FIG. 43.

[0664] Configuration Space.

[0665] The INIC is implemented as a multi-function device. The firstdevice is the network controller, and the second device is the debuginterface. An alternative production embodiment may implement only thenetwork controller function. Both configuration space headers will bethe same, except for the differences noted in the following description.

[0666] Vendor ID—This field will contain the Alacritech Vendor ID. Onefield will be used for both functions. The Alacritech Vendor ID is hex139A.

[0667] Device ID—Chosen at Alacritech on a device specific basis. Onefield will be used for both functions.

[0668] Command—Initialized to 00. All bits defined below as not enabled(0) will remain 0. Those that are enabled will be set to 0 or 1depending on the state of the system. Each function (network and debug)will have its own command field, as shown in FIG. 44.

[0669] Status—This is not initialized to zero. Each function will haveits own field. The configuration is as shown in FIG. 45.

[0670] Revision ID—The revision field will be shared by both functions.

[0671] Class Code—This is 02 00 00 for the network controller, and forthe debug interface. The field will be shared.

[0672] Cache Line Size—This is initialized to zero. Supported sizes are16, 32, 64 and 128 bytes. This hardware register is replicated in SRAMand supported separately for each function, but THE MICROPROCESSOR willimplement the value set in Configuration Space 1 (the networkprocessor).

[0673] Latency Timer—This is initialized to zero. The function issupported. This hardware register is replicated in SRAM. Each functionis supported separately, but THE MICROPROCESSOR will implement the valueset in Configuration Space 1 (the network processor).

[0674] Header Type—This is set to 80 for both functions, but will besupported separately.

[0675] BIST—Is implemented. In addition to responding to a request torun self test, if test after reset fails, a code will be set in the BISTregister. This will be implemented separately for each function.

[0676] Base Address Register—A single base address register isimplemented for each function. It is 64 bits in length, and the bottomfour bits are configured as follows: Bit 0-0, indicates memory baseaddress; Bit 1,2-00, locate base address anywhere in 32 bit memoryspace; and Bit 3-1, memory is prefetchable.

[0677] CardBus CIS Pointer—Not implemented-initialized to 0.

[0678] Subsystem Vendor ID—Not implemented-initialized to 0.

[0679] Subsystem ID—Not implemented-initialized to 0.

[0680] Expansion ROM Base Address—Not implemented-initialized to 0.

[0681] Interrupt Line—Implemented-initialized to 0. This is implementedseparately for each function.

[0682] Interrupt Pin—This is set to 01, corresponding to INTA# for thenetwork controller, and 02, corresponding to INTB# for the debuginterface. This is implemented separately for each function.

[0683] Min_Gnt—This can be set at a value in the range of 10, to allowreasonably long bursts on the bus. This is implemented separately foreach function.

[0684] Max_Lat—This can be set to 0 to indicate no particularrequirement for frequency of access to PCI. This is implementedseparately for each function.

[0685] Memory Space.

[0686] Because each of the following functions may or may not reside ina single location, and may or may not need to be in SRAM at all, theaddress for each is really only used as an identifier (label). There is,therefore, no control block anywhere in memory that represents thismemory space. When the host writes one of these registers, the utilityprocessor will construct the data required and transfer it. Reads tothis memory will generate 00 for data.

[0687] Network Processor.

[0688] The following four byte registers, beginning at location h00 ofthe network processor's allocated memory, are defined.

[0689]00—Interrupt Status Pointer—Initialized by the host to point to afour byte area where status is stored.

[0690]04—Interrupt Status—Returned status from host. Sent after one ormore status conditions have been reset. Also an interlock for storingany new status. Once status has been stored at the Interrupt StatusPointer location, no new status will be ORed until the host writes theInterrupt Status Register. New status will be ored with any remaininguncleared status (as defined by the contents of the returned status) andstored again at the Interrupt Status Pointer location. Bits are asfollows:

[0691] Bit 31—ERR—Error bits are set;

[0692] Bit 30—RCV—Receive has occurred;

[0693] Bit 29—XMT—Transmit command complete; and

[0694] Bit 25 RMISS—Receive drop occurred due to no buffers.

[0695]08—Interrupt Mask—Written by the host. Interrupts are masked foreach of the bits in the interrupt status when the same bit in the maskregister is set. When the Interrupt Mask register is written and as aresult a status bit is unmasked, an interrupt is generated. Also, whenthe Interrupt Status Register is written, enabling new status to bestored, when it is stored if a bit is stored that is not masked by theInterrupt Mask, an interrupt is generated.

[0696]0C—Header Buffer Address—Written by host to pass a set of headerbuffers to the INIC.

[0697]10—Data Buffer Handle—First register to be written by the Host totransfer a receive data buffer to the INIC. This data is Host referencedata. It is not used by the INIC, it is returned with the data buffer.However, to insure integrity of the buffer, this register must beinterlocked with the Data Buffer Address register. Once the Data BufferAddress register has been written, neither register can be written untilafter the Data Buffer Handle register has been read by THEMICROPROCESSOR.

[0698]14—Data Buffer Address—Pointer to the data buffer being sent tothe INIC by the Host. Must be interlocked with the Data Buffer Handleregister.

[0699]18—Command Buffer Address XMT0—Pointer to a set of command bufferssent by the Host. THE MICROPROCESSOR will DMA the, buffers to local DRAMfound on the FreeSType queue and queue the Command Buffer Address XMT0with the local address replacing the host Address.

[0700]1C—Command Buffer Address SMT1.

[0701]20—Command Buffer Address SMT2.

[0702]24—Command Buffer Address SMT3.

[0703]28—Response Buffer Address—Pointer to a set of response bufferssent by the Host. These will be treated in the same fashion as theCommand Buffer Address registers.

[0704] Utility Processor.

[0705] Ending status will be handled by the utility processor in thesame fashion as it is handled by the network processor. At present twoending status conditions are defined B31—command complete, andB30—error. When end status is stored an interrupt is generated.

[0706] Two additional registers are defined, Command Pointer and DataPointer. The Host is responsible for insuring that the Data Pointer isvalid and points to sufficient memory before storing a command pointer.Storing a command pointer initiates command decode and execution by thedebug processor. The Host must not modify either command or Data Pointeruntil ending status has been received, at which point a new command maybe initiated. Memory space is write only by the Host, reads will receive00. The format is as follows:

[0707]00—Interrupt Status Pointer—Initialized by the host to point to afour byte area where status is stored.

[0708]04—Interrupt Status—Returned status from host. Sent after one ormore status conditions have been reset. Also an interlock for storingany new status. Once status has been stored at the Interrupt StatusPointer location, no new status will be stored until the host writes theInterrupt Status Register. New status will be ored with any remaininguncleared status (as defined by the contents of the returned status) andstored again at the Interrupt Status Pointer location. Bits are asfollows:

[0709] Bit 31—CC—Command Complete;

[0710] Bit 30—ERR—Error;

[0711] Bit29—Transmit Processor Halted;

[0712] Bit28—Receive Processor Halted; and

[0713] Bit27—Utility Processor Halted.

[0714]08—Interrupt Mask—Written by the host. Interrupts are masked foreach of the bits in the interrupt status when the same bit in the maskregister is set. When the Interrupt Mask register is written and as aresult a status bit is unmasked, an interrupt is generated. Also, whenthe Interrupt Status Register is written, enabling new status to bestored, when it is stored if a bit is stored that is not masked by theInterrupt Mask, an interrupt is generated.

[0715]0C—Command Pointer—Points to command to be executed. Storing thispointer initiates command decode and execution.

[0716]10—Data Pointer—Points to the data buffer. This is used for bothread and write data, determined by the command function.

[0717] Debug Interface.

[0718] In order to provide a mechanism to debug the microcode running onthe microprocessor sequencers, a debug process has been defined whichwill run on the utility sequencer. This processor will interface with acontrol program on the host processor over PCI.

[0719] PCI Interface.

[0720] This interface is defined in the combination of the UtilityProcessor and the Host Interface Strategy sections, above.

[0721] Command Format.

[0722] The first byte of the command, the command byte, defines thestructure of the remainder of the command.

[0723] Command Byte.

[0724] The first five bits of the command byte are the command itself.The next bit is used to specify an alternate processor, and the last twobits specify which processors are intended for the command.

[0725] Processor Bits.

[0726]00—Any Processor;

[0727]01—Transmit Processor;

[0728]10—Receive Processor; and

[0729]11—Utility Processor.

[0730] Alternate Processor.

[0731] This bit defines which processor should handle debug processingif the utility processor is defined as the processor in debug.

[0732]0—Transmit Processor; and

[0733]1—Receive Processor.

[0734] Single Byte Commands.

[0735]00—Halt—This command asynchronously halts the processor.

[0736]08—Run—This command starts the processor.

[0737]10—Step—This command steps the processor.

[0738] Eight Byte Commands. 18 - Break 0 1 2-3 4-7 Command ReservedCount Address

[0739] This command sets a stop at the specified address. A count of 1causes the specified processor to halt the first time it executes theinstruction. A count of 2 or more causes the processor to halt afterthat number of executions. The processor is halted just before executingthe instruction. A count of 0 does not halt the processor, but causes async signal to be generated. If a second processor is set to the samebreak address, the count data from the first break request is used, andeach time either processor executes the instruction the count isdecremented. 20 - Reset Break 0 1-3 4-7 Command Reserved Address

[0740] This command resets a previously set break point at the specifiedaddress. Reset break fully resets that address. If multiple processorswere set to that break point, all will be reset. 28 - Dump 0 1 2-3 4-7Command Descriptor Count Address

[0741] This command transfers to the host the contents of thedescriptor. For descriptors larger than four bytes, a count, in fourbyte increments is specified. For descriptors utilizing an address theaddress field is specified.

[0742] Descriptor.

[0743]00—Register—This descriptor uses both count and address fields.Both fields are four byte based (a count of 1 transfers four bytes).

[0744]01—Sram—This descriptor uses both count and address fields. Countis in four byte blocks. Address is in bytes, but if it is not four bytealigned, it is forced to the lower four byte aligned address.

[0745]02—DRAM—This descriptor uses both count and address fields. Countis in four byte blocks. Address is in bytes, but if it is not four bytealigned, it is forced to the lower four byte aligned address.

[0746]03—Cstore—This descriptor uses both count and address fields.Count is in four byte blocks. Address is in bytes, but if it is not fourbyte aligned, it is forced to the lower four byte aligned address.

[0747] Stand-alone descriptors: The following descriptors do not useeither the count or address fields. They transfer the contents of thereferenced register.

[0748]04—CPU_STATUS;

[0749]05—PC;

[0750]06—ADDR_REGA;

[0751]07—ADDR_REGB;

[0752]08—RAM_BASE;

[0753]09—FILE_BASE;

[0754]0A—INSTR_REG_L;

[0755]0B—INSTR_REG_H;

[0756]0C—MAC_DATA;

[0757]0D—DMA_EVENT;

[0758]0E—MISC_EVENT;

[0759]0F—Q_IN_RDY;

[0760]10—Q_OUT_RDY;

[0761]11—LOCK STATUS;

[0762]12—STACK—This returns 12 bytes; and

[0763]13—SENSE_REG.

[0764] This register contains four bytes of data. If error status isposted for a command, if the next command that is issued reads thisregister, a code describing the error in more detail may be obtained. Ifany command other than a dump of this register is issued after errorstatus, sense information will be reset. 30 - Load 0 1 2-3 4-7 CommandDescriptor Count Address

[0765] This command transfers from the host the contents of thedescriptor. For descriptors larger than four bytes, a count, in fourbyte increments is specified. For descriptors utilizing an address theaddress field is specified.

[0766] Descriptor.

[0767]00—Register—This descriptor uses both count and address fields.Both fields are four byte based.

[0768]01—Sram—This descriptor uses both count and address fields. Countis in four byte blocks. Address is in bytes, but if it is not four bytealigned, it is forced to the lower four byte aligned address.

[0769]02—DRAM—This descriptor uses both count and address fields. Countis in four byte blocks. Address is in bytes, but if it is not four bytealigned, it is forced to the lower four byte aligned address.

[0770]03—Cstore—This descriptor uses both count and address fields.Count is in four byte blocks. Address is in bytes, but if it is not fourbyte aligned, it is forced to the lower four byte aligned address. Thisapplies to WCS only.

[0771] Stand-alone descriptors: The following descriptors do not useeither the count or address fields. They transfer the contents of thereferenced register.

[0772]04—ADDR_REGA;

[0773]05—ADDR_REGB;

[0774]06—RAM_BASE;

[0775]07—FILE_BASE;

[0776]08—MAC_DATA;

[0777]09—Q_IN_RDY;

[0778]0A—Q_OUT_RDY;

[0779]0B—DBG_ADDR; and

[0780]38—MAP.

[0781] This command allows an instruction in ROM to be replaced by aninstruction in WCS. The new instruction will be located in the Hostbuffer. It will be stored in the first eight bytes of the buffer, withthe high bits unused. To reset a mapped out instruction, map it tolocation 00. 0 1-3 4-7 Command Address to Address to Map To Map Out

[0782] Hardware Specification.

[0783] Features:

[0784] 1) Peripheral Component Interconnect (PCI) Interface.

[0785] a) Universal PCI interface supports both 5.0V and 3.3V signalingenvironments;

[0786] b) Supports both 32-bit and 64 bit PCI interface;

[0787] c) Supports PCI clock frequencies from 15 MHz to 66 MHz;

[0788] d) High performance bus mastering architecture;

[0789] e) Host memory based communications reduce register accesses;

[0790] f) Host memory based interrupt status word reduces registerreads;

[0791] g) Plug and Play compatible;

[0792] h) PCI specification revision 2.1 compliant;

[0793] i) PCI bursts up to 512 bytes;

[0794] j) Supports cache line operations up to 128 bytes;

[0795] k) Both big-endian and little-endian byte alignments supported;and

[0796] l) Supports Expansion ROM.

[0797] 2) Network Interface.

[0798] a) Four internal 802.3 and ethernet compliant Macs;

[0799] b) Media Independent Interface (MII) supports external PHYs;

[0800] c) 10BASE-T, 100BASE-TX/FX and 100BASE-T4 supported;

[0801] d) Full and half-duplex modes supported;

[0802] e) Automatic PHY status polling notifies system of status change;

[0803] f) Provides SNMP statistics counters;

[0804] g) Supports broadcast and multicast packets;

[0805] h) Provides promiscuous mode for network monitoring or multipleunicast address detection;

[0806] i) Supports “huge packets” up to 32 KB;

[0807] j) Mac-layer loop-back test mode; and

[0808] k) Supports auto-negotiating Phys.

[0809] 3) Memory Interface.

[0810] a) External DRAM buffering of transmit and receive packets;

[0811] b) Buffering configurable as 4 MB, 8 MB, 16 MB or 32 MB;

[0812] c) 32-bit interface supports throughput of 224 MB/s;

[0813] d) Supports external FLASH ROM up to 4 MB, for diskless bootapplications; and

[0814] e) Supports external serial EEPROM for custom configuration andMac addresses.

[0815] 4) Protocol Processor.

[0816] a) High speed, custom, 32-bit processor executes 66 millioninstructions per second;

[0817] b) Processes IP, TCP and NETBIOS protocols;

[0818] c) Supports up to 256 resident TCP/IP contexts; and

[0819] d) Writable control store (WCS) allows field updates for featureenhancements.

[0820] 5) Power.

[0821] a) 3.3V chip operation; and

[0822] b) PCI controlled 5.0V/3.3V I/O cell operation.

[0823] 6) Packaging.

[0824] a) 272-pin plastic ball grid array;

[0825] b) 91 PCI signals;

[0826] c) 68 MII signals;

[0827] d) 58 external memory signals;

[0828] e) 1 clock signal;

[0829] f) 54 signals split between power and ground; and

[0830] g) 272 total pins.

[0831] General Description.

[0832] The microprocessor (see FIG. 46) is a 32-bit, full-duplex, fourchannel, 10/100-Megabit per second (Mbps), Intelligent Network InterfaceController (INIC), designed to provide high-speed protocol processingfor server applications. It combines the functions of a standard networkinterface controller and a protocol processor within a single chip.Although designed specifically for server applications, themicroprocessor can be used by PCs, workstations and routers or anywherethat TCP/IP protocols are being utilized.

[0833] When combined with four 802.3/MII compliant Phys and SynchronousDRAM (SDRAM), the INIC comprises four complete ethernet nodes. Itcontains four 802.3/ethernet compliant Macs, a PCI Bus Interface Unit(BIU), a memory controller, transmit fifos, receive fifos and a customTCP/IP/NETBIOS protocol processor. The INIC supports 10Base-T,100Base-TX, 100Base-FX and 100Base-T4 via the MII interface attachmentof appropriate Phys.

[0834] The INIC Macs provide statistical information that may be usedfor SNMP. The Macs operate in promiscuous mode allowing the INIC tofunction as a network monitor, receive broadcast and multicast packetsand implement multiple Mac addresses for each node.

[0835] Any 802.3/MII compliant PHY can be utilized, allowing the INIC tosupport 10BASE-T, 10BASE-T2, 100BASE-TX, 100Base-FX and 100BASE-T4 aswell as future interface standards. PHY identification andinitialization is accomplished through host driver initializationroutines. PHY status registers can be polled continuously by the INICand detected PHY status changes reported to the host driver. The Mac canbe configured to support a maximum frame size of 1518 bytes or 32768bytes.

[0836] The 64-bit, multiplexed BIU provides a direct interface to thePCI bus for both slave and master functions. The INIC is capable ofoperating in either a 64-bit or 32-bit PCI environment, while supporting64-bit addressing in either configuration. PCI bus frequencies up to 66MHz are supported yielding instantaneous bus transfer rates of 533 MB/s.Both 5.0V and 3.3V signaling environments can be utilized by the INIC.Configurable cache-line size up to 256 B will accommodate futurearchitectures, and Expansion ROM/Flash support allows for disklesssystem booting. Non-PC applications are supported via programmable bigand little endian modes. Host based communication has been utilized toprovide the best system performance possible.

[0837] The INIC supports Plug-N-Play auto-configuration through the PCIconfiguration space. External pull-up and pull-down resistors, on thememory I/O pins, allow selection of various features during chip reset.Support of an external eeprom allows for local storage of configurationinformation such as Mac addresses.

[0838] External SDRAM provides frame buffering, which is configurable as4 MB, 8 MB, 16 MB or 32 MB using the appropriate SIMMs. Use of −10 speedgrades yields an external buffer bandwidth of 224 MB/s. The bufferprovides temporary storage of both incoming and outgoing frames. Theprotocol processor accesses the frames within the buffer in order toimplement TCP/IP and NETBIOS. Incoming frames are processed, assembledthen transferred to host memory under the control of the protocolprocessor. For transmit, data is moved from host memory to buffers wherevarious headers are created before being transmitted out via the Mac.

[0839] 1) Cores/Cells.

[0840] a) LSI Logic Ethernet—110 Core, 100Base and 10Base Mac with MIIinterface;

[0841] b) LSI Logic single port SRAM, triple port SRAM and ROMavailable;

[0842] c) LSI Logic PCI 66 MHz, 5V compatible I/O cell; and

[0843] d) LSI Logic PLL.

[0844] 2) Die Size/Pin Count.

[0845] LSI Logic G10 process. FIG. 47 shows the area on the die of eachmodule.

[0846] 3) Datapath Bandwidth (See FIG. 48).

[0847] 4) CPU Bandwidth (See FIG. 49).

[0848] 5) Performance Features.

[0849] a) 512 registers improve performance through reduced scratch ramaccesses and reduced instructions;

[0850] b) Register windowing eliminates context-switching overhead;

[0851] c) Separate instruction and data paths eliminate memorycontention;

[0852] d) Totally resident control store eliminates stalling duringinstruction fetch;

[0853] e) Multiple logical processors eliminate context switching andimprove real-time response;

[0854] f) Pipelined architecture increases operating frequency;

[0855] g) Shared register and scratch ram improve inter-processorcommunication;

[0856] h) Fly-by state-Machine assists address compare and checksumcalculation;

[0857] i) TCP/IP-context caching reduces latency;

[0858] j) Hardware implemented queues reduce CPU overhead and latency;

[0859] k) Horizontal microcode greatly improves instruction efficiency;

[0860] l) Automatic frame DMA and status between Mac and DRAM buffer;and

[0861] m) Deterministic architecture coupled with context switchingeliminates processor stalls.

[0862] Processor.

[0863] The processor is a convenient means to provide a programmablestate-machine which is capable of processing incoming frames, processinghost commands, directing network traffic and directing PCI bus traffic.Three processors are implemented using shared hardware in a three-levelpipelined architecture which launches and completes a single instructionfor every clock cycle. The instructions are executed in three distinctphases corresponding to each of the pipeline stages where each phase isresponsible for a different function.

[0864] The first instruction phase writes the instruction results of thelast instruction to the destination operand, modifies the programcounter (Pc), selects the address source for the instruction to fetch,then fetches the instruction from the control store. The fetchedinstruction is then stored in the instruction register at the end of theclock cycle.

[0865] The processor instructions reside in the on-chip control-store,which is implemented as a mixture of ROM and SRAM. The ROM contains 1 Kinstructions starting at address 0x0000 and aliases each 0x0400locations throughout the first 0x8000 of instruction space. The SRAM(WCS) will hold up to 0x2000 instructions starting at address 0x8000 andaliasing each 0x2000 locations throughout the last 0x8000 of instructionspace. The ROM and SRAM are both 49-bits wide accounting for bits [48:0]of the instruction microword. A separate mapping ram provides bits[55:49] of the microword (MapAddr) to allow replacement of faulty ROMbased instructions. The mapping ram has a configuration of 128×7 whichis insufficient to allow a separate map address for each of the 1 K ROMlocations. To allow re-mapping of the entire 1 K ROM space, the map ramaddress lines are connected to the address bits Fetch[9:3]. The resultis that the ROM is re-mapped in blocks of 8 contiguous locations.

[0866] The second instruction phase decodes the instruction which wasstored in the instruction register. It is at this point that the mapaddress is checked for a non-zero value which will cause the decoder toforce a Jmp instruction to the map address. If a non-zero value isdetected then the decoder selects the source operands for the Aluoperation based on the values of the OpdASel, OpdBSel and AluOp fields.These operands are then stored in the decode register at the end of theclock cycle. Operands may originate from File, SRAM, or flip-flop basedregisters. The second instruction phase is also where the results of theprevious instruction are written to the SRAM.

[0867] The third instruction phase is when the actual Alu operation isperformed, the test condition is selected and the Stack push and pop areimplemented. Results of the Alu operation are stored in the resultsregister at the end of the clock cycle.

[0868]FIG. 50 is a block diagram of the CPU. FIG. 50 shows the hardwarefunctions associated with each of the instruction phases. Note thatvarious functions have been distributed across the three phases of theinstruction execution in order to minimize the combinatorial delayswithin any given phase.

[0869] Instruction Set.

[0870] The micro-instructions are divided into six types according tothe program control directive. The micro-instruction is further dividedinto sub-fields for which the definitions are dependent upon theinstruction type. The six instruction types are listed in FIG. 51.

[0871] All instructions (see FIG. 51) include the Alu operation (AluOp),operand “A” select (OpdASel), operand “B” select (OpdBSel) and Literalfields. Other field usage depends upon the instruction type.

[0872] The “jump condition code” (Jcc) instruction causes the programcounter to be altered if the condition selected by the “test select”(TstSel) field is asserted. The new program counter (Pc) value is loadedfrom either the Literal field or the AluOut as described in thefollowing section and the Literal field may be used as a source for theAlu or the ram address if the new Pc value is sourced by the Alu.

[0873] The “jump” (Jmp) instruction causes the program counter to bealtered unconditionally. The new program counter (Pc) value is loadedfrom either the Literal field or the AluOut as described in thefollowing section. The format allows instruction bits 23:16 to be usedto perform a flag operation and the Literal field may be used as asource for the Alu or the ram address if the new Pc value is sourced bythe Alu.

[0874] The “jump subroutine” (Jsr) instruction causes the programcounter to be altered unconditionally. The new program counter (Pc)value is loaded from either the Literal field or the AluOut as describedin the following section. The old program counter value is stored on thetop location of the Pc-Stack which is implemented as a LIFO memory. Theformat allows instruction bits 23:16 to be used to perform a flagoperation and the Literal field may be used as a source for the Alu orthe ram address if the new Pc value is sourced by the Alu.

[0875] The “Nxt” (Nxt) instruction causes the program counter toincrement. The format allows instruction bits 23:16 to be used toperform a flag operation and the Literal field may be used as a sourcefor the Alu or the ram address.

[0876] The “return from subroutine” (Rts) instruction is a special formof the Nxt instruction in which the “flag operation” (FIgSel) field isset to a value of Ohff. The current Pc value is replaced with the lastvalue stored in the stack. The Literal field may be used as a source forthe Alu or the ram address.

[0877] The Map instruction is provided to allow replacement ofinstructions which have been stored in ROM and is implemented any timethe “map enable” (MapEn) bit has been set and the content of the “mapaddress” (MapAddr) field is non-zero. The instruction decoder forces ajump instruction with the Alu operation and destination fields set topass the MapAddr field to the program control block.

[0878] The program control is determined by a combination of PgmCtrl,DstOpd, FlgSel and TstSel. The behavior of the program control isdefined with the “C-like” description in FIG. 52. FIGS. 53-61 show ALUoperations, selected operands, selected tests, and flag operations.

[0879] SRAM Control Sequencer (SramCtrl).

[0880] SRAM is the nexus for data movement within the INIC. A hierarchyof sequencers, working in concert, accomplish the movement of databetween DRAM, SRAM, CPU, ethernet and the Pci bus. Slave sequencers,provided with stimulus from master sequencers, request data movementoperations by way of the SRAM, Pci bus, DRAM and Flash. The slavesequencers prioritize, service and acknowledge the requests.

[0881] The data flow block diagram of FIG. 62 shows all of the masterand slave sequencers of the INIC product. Request information such asr/w, address, size, endian and alignment are represented by each requestline. Acknowledge information to master sequencers include only the sizeof the transfer being acknowledged.

[0882] The block diagram of FIG. 63 illustrates how data movement isaccomplished for a Pci slave write to DRAM. Note that the Psi (Pci slavein) module functions as both a master sequencer. Psi sends a writerequest to the SramCtrl module. Psi requests Xwr to move data from SRAMto DRAM. Xwr subsequently sends a read request to the SramCtrl modulethen writes the data to the DRAM via the Xctrl module. As each piece ofdata is moved from the SRAM to Xwr, Xwr sends an acknowledge to the Psimodule.

[0883] The SRAM control sequencer services requests to store to, orretrieve data from an SRAM organized as 1024 locations by 128 bits (16KB). The sequencer operates at a frequency of 133 MHz, allowing both aCPU access and a DMA access to occur during a standard 66 MHz CPU cycle.One 133 MHz cycle is reserved for CPU accesses during each 66 MHz cyclewhile the remaining 133 MHz cycle is reserved for DMA accesses on aprioritized basis.

[0884] The block diagram of FIG. 64 shows the major functions of theSRAM control sequencer. A slave sequencer begins by asserting a requestalong with r/w, ram address, endian, data path size, data path alignmentand request size. SramCtrl prioritizes the requests. The requestparameters are then selected by a multiplexer which feeds the parametersto the SRAM via a register. The requestor provides the SRAM addresswhich when coupled with the other parameters controls the input andoutput alignment. SRAM outputs are fed to the output aligner via aregister. Requests are acknowledged in parallel with the returned data.

[0885]FIG. 65 is a timing diagram depicting two ram accesses during asingle 66 MHz clock cycle.

[0886] External Memory Control (Xctrl).

[0887] Xctrl (See FIG. 66) provides the facility whereby Xwr, Xrd, Dcfgand Eectrl access external Flash and DRAM. Xctrl includes an arbiter,i/o registers, data multiplexers, address multiplexers and controlmultiplexers. Ownership of the external memory interace is requested byeach block and granted to each of the requesters by the arbiterfunction. Once ownership has been granted the multiplexers select theaddress, data and control signals from owner, allowing access toexternal memory.

[0888] External Memory Read Sequencer (Xrd).

[0889] The Xrd sequencer acts only as a slave sequencer. Servicingrequests issued by master sequencers, the Xrd sequencer moves data fromexternal SDRAM or flash to the SRAM, via the Xctrl module, in blocks of32 bytes or less. The nature of the SDRAM requires fixed burst sizes foreach of it's internal banks with ras precharge intervals between eachaccess. By selecting a burst size of 32 bytes for SDRAM reads andinterleaving bank accesses on a 16 byte boundary, we can ensure that theras precharge interval for the first bank is satisfied before burstcompletion for the second bank, allowing us to re-instruct the firstbank and continue with uninterrupted DRAM access. SDRAMs require aconsistent burst size be utilized each and every time the SDRAM isaccessed. For this reason, if an SDRAM access does not begin or end on a32 byte boundary, SDRAM bandwidth will be reduced due to less than 32bytes of data being transferred during the burst cycle.

[0890]FIG. 67 depicts the major functional blocks of the Xrd externalmemory read sequencer. The first step in servicing a request to movedata from SDRAM to SRAM is the prioritization of the master sequencerrequests. Next the Xrd sequencer takes a snapshot of the DRAM readaddress and applies configuration information to determine the correctbank, row and column address to apply. Once sufficient data has beenread, the Xrd sequencer issues a write request to the SramCtrl sequencerwhich in turn sends an acknowledge to the Xrd sequencer. The Xrdsequencer passes the acknowledge along to the level two master with asize code indicating how much data was written during the SRAM cycleallowing the update of pointers and counters. The DRAM read and SRAMwrite cycles repeat until the original burst request has been completedat which point the Xrd sequencer prioritizes any remaining requests inpreparation for the next burst cycle.

[0891] Contiguous DRAM burst cycles are not guaranteed to the Xrdsequencer as an algorithm is implemented which ensures highest priorityto refresh cycles followed by flash accesses, DRAM writes then DRAMreads.

[0892]FIG. 68 is a timing diagram illustrating how data is read fromSDRAM. The DRAM has been configured for a burst of four with a latencyof two clock cycles. Bank A is first selected/activated followed by aread command two clock cycles later. The bank select/activate for bank Bis next issued as read data begins returning two clocks after the readcommand was issued to bank A. Two clock cycles before we need to receivedata from bank B we issue the read command. Once all 16 bytes have beenreceived from bank A we begin receiving data from bank B.

[0893] External Memory Write Sequencer (Xwr).

[0894] The Xwr sequencer is a slave sequencer. Servicing requests issuedby master sequencers, the Xwr sequencer moves data from SRAM to theexternal SDRAM or flash, via the Xctrl module, in blocks of 32 bytes orless while accumulating a checksum of the data moved. The nature of theSDRAM requires fixed burst sizes for each of it's internal banks withras precharge intervals between each access. By selecting a burst sizeof 32 bytes for SDRAM writes and interleaving bank accesses on a 16 byteboundary, we can ensure that the ras prechage interval for the firstbank is satisfied before burst completion for the second bank, allowingus to re-instruct the first bank and continue with uninterrupted DRAMaccess. SDRAMs require a consistent burst size be utilized each andevery time the SDRAM is accessed. For this reason, if an SDRAM accessdoes not begin or end on a 32 byte boundary, SDRAM bandwidth will bereduced due to less than 32 bytes of data being transferred during theburst cycle.

[0895]FIG. 69 depicts the major functional blocks of the Xwr sequencer.The first step in servicing a request to move data from SRAM to SDRAM isthe prioritization of the level two master requests. Next the Xwrsequencer takes a Snapshot of the DRAM write address and appliesconfiguration information to determine the correct DRAM, bank, row andcolumn address to apply. The Xwr sequencer immediately issues a readcommand to the SRAM to which the SRAM responds with both data and anacknowledge. The Xwr sequencer passes the acknowledge to the level twomaster along with a size code indicating how much data was read duringthe SRAM cycle allowing the update of pointers and counters. Oncesufficient data has been read from SRAM, the Xwr sequencer issues awrite command to the DRAM starting the burst cycle and computing achecksum as the data flys by. The SRAM read cycle repeats until theoriginal burst request has been completed at which point the Xwrsequencer prioritizes any remaining requests in preparation for the nextburst cycle.

[0896] Contiguous DRAM burst cycles are not guaranteed to the Xwrsequencer as an algorithm is implemented which ensures highest priorityto refresh cycles followed by flash accesses then DRAM writes.

[0897]FIG. 70 is a timing diagram illustrating how data is written toSDRAM. The DRAM has been configured for a burst of four with a latencyof two clock cycles. Bank A is first selected/activated followed by awrite command two clock cycles later. The bank select/activate for bankB is next issued in preparation for issuing the second write command. Assoon as the first 16 byte burst to bank A completes we issue the writecommand for bank B and begin supplying data.

[0898] PCI Master-Out Sequencer (Pmo).

[0899] The Pmo sequencer (See FIG. 71) acts only as a slave sequencer.Servicing requests issued by master sequencers, the Pmo sequencer movesdata from an SRAM based fifo to a Pci target, via the PciMstrIO module,in bursts of up to 256 bytes. The nature of the PCI bus dictates the useof the write line command to ensure optimal system performance. Thewrite line command requires that the Pmo sequencer be capable oftransferring a whole multiple (1×, 2×, 3×, . . . ) of cache lines ofwhich the size is set through the Pci configuration registers. Toaccomplish this end, Pmo will automatically perform partial bursts untilit has aligned the transfers on a cache line boundary at which time itwill begin usage of the write line command. The SRAM fifo depth, of 256bytes, has been chosen in order to allow Pmo to accommodate cache linesizes up to 128 bytes. Provided the cache line size is less than 128bytes, Pmo will perform multiple, contiguous cache line bursts until ithas exhausted the supply of data.

[0900] Pmo receives requests from two separate sources; the DRAM to Pci(D2p) module and the SRAM to Pci (S2p) module. An operation first beginswith prioritization of the requests where the S2p module is givenhighest priority. Next, the Pmo module takes a Snapshot of the SRAM fifoaddress and uses this to generate read requests for the SramCtrlsequencer. The Pmo module then proceeds to arbitrate for ownership ofthe Pci bus via the PciMstrIO module. Once the Pmo holding registershave sufficient data and Pci bus mastership has been granted, the Pmomodule begins transferring data to the Pci target. For each successfultransfer, Pmo sends an acknowledge and encoded size to the mastersequencer, allow it to update it's internal pointers, counters andstatus. Once the Pci burst transaction has terminated, Pmo parks on thePci bus unless another initiator has requested ownership. Pmo againprioritizes the incoming requests and repeats the process.

[0901] PCI Master-Out Sequencer (Pmi).

[0902] The Pmi sequencer (See FIG. 72) acts only as a slave sequencer.Servicing requests issued by master sequencers, the Pmi sequencer movesdata from a Pci target to an SRAM based fifo, via the PciMstrIO module,in bursts of up to 256 bytes. The nature of the PCI bus dictates the useof the read multiple command to ensure optimal system performance. Theread multiple command requires that the Pmi sequencer be capable oftransferring a cache line or more of data. To accomplish this end, Pmiwill automatically perform partial cache line bursts until it hasaligned the transfers on a cache line boundary at which time it willbegin usage of the read multiple command. The SRAM fifo depth, of 256bytes, has been chosen in order to allow Pmi to accommodate cache linesizes up to 128 bytes. Provided the cache line size is less than 128bytes, Pmi will perform multiple, contiguous cache line bursts until ithas filled the fifo.

[0903] Pmi receive requests from two separate sources; the Pci to DRAM(P2d) module and the Pci to SRAM (P2s) module. An operation first beginswith prioritization of the requests where the P2s module is givenhighest priority. The Pmi module then proceeds to arbitrate forownership of the Pci bus via the PciMstrIO module. Once the Pci busmastership has been granted and the Pmi holding registers havesufficient data, the Pmi module begins transferring data to the SRAMfifo. For each successful transfer, Pmi sends an acknowledge and encodedsize to the master sequencer, allowing it to update it's internalpointers, counters and status. Once the Pci burst transaction hasterminated, Pmi parks on the Pci bus unless another initiator hasrequested ownership. Pmi again prioritizes the incoming requests andrepeats the process.

[0904] DRAM to PCI Sequencer (D2p).

[0905] The D2p sequencer (See FIG. 73) acts is a master sequencer.Servicing channel requests issued by the CPU, the D2p sequencer managesmovement of data from DRAM to the Pci bus by issuing requests to boththe Xrd sequencer and the Pmo sequencer. Data transfer is accomplishedusing an SRAM based fifo through which data is staged.

[0906] D2p can receive requests from any of the processor's thirty-twoDMA channels. Once a command request has been detected, D2p fetches aDMA descriptor from an SRAM location dedicated to the requesting channelwhich includes the DRAM address, Pci address, Pci endian and requestsize. D2p then issues a request to the D2s sequencer causing the SRAMbased fifo to fill with DRAM data. Once the fifo contains sufficientdata for a Pci transaction, D2s issues a request to Pmo which in turnmoves data from the fifo to a Pci target. The process repeats until theentire request has been satisfied at which time D2p writes ending statusin to the SRAM DMA descriptor area and sets the channel done bitassociated with that channel. D2p then monitors the DMA channels foradditional requests. FIG. 74 is an illustration showing the major blocksinvolved in the movement of data from DRAM to Pci target.

[0907] PCI to DRAM Sequencer (P2d).

[0908] The P2d sequencer (See FIG. 75) acts as both a slave sequencerand a master sequencer. Servicing channel requests issued by the CPU,the P2d sequencer manages movement of data from Pci bus to DRAM byissuing requests to both the Xwr sequencer and the Pmi sequencer. Datatransfer is accomplished using an SRAM based fifo through which data isstaged.

[0909] P2d can receive requests from any of the processor's thirty-twoDMA channels. Once a command request has been detected, P2d, operatingas a slave sequencer, fetches a DMA descriptor from an SRAM locationdedicated to the requesting channel which includes the DRAM address, Pciaddress, Pci endian and request size. P2d then issues a request to Pmowhich in turn moves data from the Pci target to the SRAM fifo. Next, P2dissues a request to the Xwr sequencer causing the SRAM based fifocontents to be written to the DRAM. The process repeats until the entirerequest has been satisfied at which time P2d writes ending status in tothe SRAM DMA descriptor area and sets the channel done bit associatedwith that channel. P2d then monitors the DMA channels for additionalrequests. FIG. 76 is an illustration showing the major blocks involvedin the movement of data from a Pci target to DRAM.

[0910] SRAM to PCI Sequencer (S2p).

[0911] The S2p sequencer (See FIG. 77) acts as both a slave sequencerand a master sequencer.

[0912] Servicing channel requests issued by the CPU, the S2p sequencermanages movement of data from SRAM to the Pci bus by issuing requests tothe Pmo sequencer S2p can receive requests from any of the processor'sthirty-two DMA channels. Once a command request has been detected, S2p,operating as a slave sequencers fetches a DMA descriptor from an SRAMlocation dedicated to the requesting channel which includes the SRAMaddress, Pci address, Pci endian and request size. S2p then issues arequest to Pmo which in turn moves data from the SRAM to a Pci target.The process repeats until the entire request has been satisfied at whichtime S2p writes ending status in to the SRAM DMA descriptor area andsets the channel done bit associated with that channel. S2p thenmonitors the DMA channels for additional requests. FIG. 78 is anillustration showing the major blocks involved in the movement of datafrom SRAM to Pci target.

[0913] PCI to SRAM Sequencer (P2s).

[0914] The P2s sequencer (See FIG. 79) acts as both a slave sequencerand a master sequencer.

[0915] Servicing channel requests issued by the CPU, the P2s sequencermanages movement of data from Pci bus to SRAM by issuing requests to thePmi sequencer. P2s can receive requests from any of the processor'sthirty-two DMA channels. Once a command request has been detected, P2s,operating as a slave sequencer, fetches a DMA descriptor from an SRAMlocation dedicated to the requesting channel which includes the SRAMaddress, Pci address, Pci endian and request size. P2s then issues arequest to Pmo which in turn moves data from the Pci target to the SRAM.The process repeats until the entire request has been satisfied at whichtime P2s writes ending status in to the DMA descriptor area of SRAM andsets the channel done bit associated with that channel. P2s thenmonitors the DMA channels for additional requests. FIG. 80 is anillustration showing the major blocks involved in the movement of datafrom a Pci target to DRAM.

[0916] DRAM to SRAM Sequencer (D2s).

[0917] The D2s sequencer (See FIG. 81) acts as both a slave sequencerand a master sequencer. Servicing channel requests issued by the CPU,the D2s sequencer manages movement of data from DRAM to SRAM by issuingrequests to the Xrd sequencer.

[0918] D2s can receive requests from any of the processor's thirty-twoDMA channels. Once a command request has been detected, D2s, operatingas a slave sequencer, fetches a DMA descriptor from an SRAM locationdedicated to the requesting channel which includes the DRAM address,SRAM address and request size. D2s then issues a request to the Xrdsequencer causing the transfer of data to the SRAM. The process repeatsuntil the entire request has been satisfied at which time D2s writesending status in to the SRAM DMA descriptor area and sets the channeldone bit associated with that channel. D2s then monitors the DMAchannels for additional requests. FIG. 82 is an illustration showing themajor blocks involved in the movement of data from DRAM to SRAM.

[0919] SRAM to DRAM Sequencer (S2d).

[0920] The S2d sequencer (See FIG. 83) acts as both a slave sequencerand a master sequencer. Servicing channel requests issued by the CPU,the S2d sequencer manages movement of data from SRAM to DRAM by issuingrequests to the Xwr sequencer.

[0921] S2d can receive requests from any of the processor's thirty-twoDMA channels. Once a command request has been detected, S2d, operatingas a slave sequencer, fetches a DMA descriptor from an SRAM locationdedicated to the requesting channel which includes the DRAM address,SRAM address, checksum reset and request size. S2d then issues a requestto the Xwr sequencer causing the transfer of data to the DRAM. Theprocess repeats until the entire request has been satisfied at whichtime S2d writes ending status in to the SRAM DMA descriptor area andsets the channel done bit associated with that channel. S2d thenmonitors the DMA channels for additional requests. FIG. 84 is anillustration showing the major blocks involved in the movement of datafrom SRAM to DRAM.

[0922] PCI Slave Input Sequencer (Psi).

[0923] The Psi sequencer (See FIG. 85) acts as both a slave sequencerand a master sequencer. Servicing requests issued by a Pci master, thePsi sequencer manages movement of data from Pci bus to SRAM and Pci busto DRAM via SRAM by issuing requests to the SramCtrl and Xwr sequencers.

[0924] Psi manages write requests to configuration space, expansion rom,DRAM, SRAM and memory mapped registers. Psi separates these Pci busoperations in to two categories with different action taken for each.DRAM accesses result in Psi generating write request to an SRAM bufferfollowed with a write request to the Xwr sequencer. Subsequent write orread DRAM operations are retry terminated until the buffer has beenemptied. An event notification is set for the processor allowing messagepassing to occur through DRAM space.

[0925] All other Pci write transactions result in Psi posting the writeinformation including Pci address, Pci byte marks and Pci data to areserved location in SRAM, then setting an event flag which the eventprocessor monitors. Subsequent writes or reads of configuration,expansion rom, SRAM or registers are terminated with retry until theprocessor clears the event flag. This allows the INIC pipelining levelsto a minimum for the posted write and give the processor ample time tomodify data for subsequent Pci read operations.

[0926]FIG. 85 depicts the sequence of events when Psi is the target of aPci write operation. Note that events 4 through 7 occur only when thewrite operation targets the DRAM.

[0927] PCI Slave Output Sequencer (Pso).

[0928] The Pso sequencer (See FIG. 86) acts as both a slave sequencerand a master sequencer. Servicing requests issued by a Pci master, thePso sequencer manages movement of data to Pci bus from SRAM and to Pcibus from DRAM via SRAM by issuing requests to the SramCtrl and Xrdsequencers.

[0929] Pso manages read requests to configuration space, expansion rom,DRAM, SRAM and memory mapped registers. Pso separates these Pci busoperations in to two categories with different action taken for each.DRAM accesses result in Pso generating read request to the Xrd sequencerfollowed with a read request to SRAM buffer. Subsequent write or readDRAM operations are retry terminated until the buffer has been emptied.

[0930] All other Pci read transactions result in Pso posting the readrequest information including Pci address and Pci byte marks to areserved location in SRAM, then setting an event flag which the eventprocessor monitors. Subsequent writes or reads of configuration,expansion rom, SRAM or registers are terminated with retry until theprocessor clears the event flag. This allows the INIC to use amicrocoded response mechanism to return data for the request. Theprocessor decodes the request information, formulates or fetches therequested data and stores it in SRAM then clears the event flag allowingPso to fetch the data and return it on the Pci bus.

[0931]FIG. 78 depicts the sequence of events when Pso is the target of aPci read operation.

[0932] Frame Receive Sequencer (RcvX).

[0933] The receive sequencer (See FIG. 87) (RcvSeq) analyzes and managesincoming packets, stores the result in DRAM buffers, then notifies theprocessor through the receive queue (RcvQ) mechanism. The process beginswhen a buffer descriptor is available at the output of the FreeQ. RcvSeqissues a request to the Qmg which responds by supplying the bufferdescriptor to RcvSeq. RcvSeq then waits for a receive packet. The Mac,network, transport and session information is analyzed as each byte isreceived and stored in the assembly register (AssyReg). When four bytesof information is available, RcvSeq requests a write of the data to theSRAM. When sufficient data has been stored in the SRAM based receivefifo, a DRAM write request is issued to Xwr. The process continues untilthe entire packet has been received at which point RcvSeq stores theresults of the packet analysis in the beginning of the DRAM buffer. Oncethe buffer and status have both been stored, RcvSeq issues a write-queuerequest to Qmg. Qmg responds by storing a buffer descriptor and a statusvector provided by RcvSeq. The process then repeats. If RcvSeq detectsthe arrival of a packet before a free buffer is available, it ignoresthe packet and sets the FrameLost status bit for the next receivedpacket.

[0934]FIG. 88 depicts the sequence of events for successful reception ofa packet followed by a definition of the receive buffer and the bufferdescriptor as stored on the RcvQ. FIG. 89 shows the Receive BufferDescriptor. FIGS. 90-92 show the Receive Buffer Format.

[0935] Frame Transmit Sequencer (XmtX).

[0936] The transmit sequencer (See FIG. 93) (XmtSeq) analyzes andmanages outgoing packets, using buffer descriptors retrieved from thetransmit queue (XmtQ) then storing the descriptor for the freed bufferin the free buffer queue (FreeQ). The process begins when a bufferdescriptor is available at the output of the XmtQ. XmtSeq issues arequest to the Qmg which responds by supplying the buffer descriptor toXmtSeq. XmtSeq then issues a read request to the Xrd sequencer. Next,XmtSeq issues a read request to SramCtrl then instructs the Mac to beginframe transmission. Once the frame transmission has completed, XmtSeqstores the buffer descriptor on the FreeQ thereby recycling the buffer.

[0937]FIG. 94 depicts the sequence of events for successful transmissionof a packet followed by a definition of the receive buffer and thebuffer descriptor as stored on the XmtQ. FIG. 95 shows the TransmitBuffer Descriptor. FIG. 96 shows the Transmit Buffer Format. FIG. 97shows the Transmit Status Vector.

[0938] Queue Manager (Qmg).

[0939] The INIC includes special hardware assist for the implementationof message and pointer queues. The hardware assist is called the queuemanager (See FIG. 98) (Qmg) and manages the movement of queue entriesbetween CPU and SRAM, between DMA sequencers and SRAM as well as betweenSRAM and DRAM. Queues comprise three distinct entities; the queue head(QHd), the queue tail (QTl) and the queue body (QBdy). QHd resides in 64bytes of scratch ram and provides the area to which entries will bewritten (pushed). QTl resides in 64 bytes of scratch ram and containsqueue locations from which entries will be read (popped). QBdy residesin DRAM and contains locations for expansion of the queue in order tominimize the SRAM space requirements. The QBdy size depends upon thequeue being accessed and the initialization parameters presented duringqueue initialization.

[0940] Qmg accepts operations from both CPU and DMA sources (See FIG.99). Executing these operations at a frequency of 133 MHz, Qmg reserveseven cycles for DMA requests and reserves odd cycles for CPU requests.Valid CPU operations include initialize queue (InitQ), write queue (WrQ)and read queue (RdQ). Valid DMA requests include read body (RdBdy) andwrite body (WrBdy). Qmg working in unison with Q2d and D2q generaterequests to the Xwr and Xrd sequencers to control the movement of databetween the QHd, QTl and QBdy.

[0941]FIG. 98 shows the major functions of Qmg. The arbiter selects thenext operation to be performed. The dual-ported SRAM holds the queuevariables HdWrAddr, HdRdAddr, TlWrAddr, TlRdAddr, BdyWrAddr, BdyRdAddrand QSz. Qmg accepts an operation request, fetches the queue variablesfrom the queue ram (Qram), modifies the variables based on the currentstate and the requested operation then updates the variables and issuesa read or write request to the SRAM controller. The SRAM controllerservices the requests by writing the tail or reading the head andreturning an acknowledge.

[0942] DMA Operations.

[0943] DMA operations are accomplished through a combination ofthirtytwo DMA channels (DmaCh) and seven DMA sequencers (DmaSeq). EachDMA channel provides a mechanism whereby a CPU can issue a command toany of the seven DMA sequencers. Where as the DMA channels aremulti-purpose, the DMA sequencers they command are single purpose asshown in FIG. 100.

[0944] The processors manage DMA in the following way. The processorwrites a DMA descriptor to an SRAM location reserved for the DMAchannel. The format of the DMA descriptor is dependent upon the targetedDMA sequencer. The processor then writes the DMA sequencer number to thechannel command register.

[0945] Each of the DMA sequencers polls all thirtytwo DMA channels insearch of commands to execute. Once a command request has been detected,the DMA sequencer fetches a DMA descriptor from a fixed location inSRAM. The SRAM location is fixed and is determined by the DMA channelnumber. The DMA sequencer loads the DMA descriptor in to it's ownregisters, executes the command, then overwrites the DMA descriptor withending status. Once the command has halted, due to completion or error,and the ending status has been written, the DMA sequencer sets the donebit for the current DMA channel.

[0946] The done bit appears in a DMA event register which the CPU canexamine. The CPU fetches ending status from SRAM, then clears the donebit by writing zeroes to the channel command (ChCmd) register. Thechannel is now ready to accept another command.

[0947] The format of the channel command register is as shown in FIG.101. The format of the P2d or P2s descriptor is as shown in FIG. 102.The format of the S2p or D2p descriptor is as shown in FIG. 103. Theformat of the S2d, D2d or D2s descriptor is as shown in FIG. 104. Theformat of the ending status of all channels is as shown in FIG. 105. Theformat of the ChEvnt register is as shown in FIG. 106. FIG. 107 is ablock diagram of MAC CONTROL (Macctrl).

[0948] Load Calculations.

[0949] The following load calculations are based on the following basicformulae:

N=X*R (Little's Law)

[0950] where:

[0951] N=number of jobs in the system (either in progress or in aqueue),

[0952] X=system throughput,

[0953] R=response time (which includes time waiting in queues).

U=X*S (from Little's Law)

[0954] where:

[0955] S=service time,

[0956] U=utilization.

R=S/(1−U)

[0957] for exponential service times (which is the worst-caseassumption).

[0958] A 256-byte frame at 100 Mb/sec takes 20 usec per frame.

[0959] 4*100 Mbit ethernets receiving at full frame rate is:

[0960] 51200 (4*12800) frames/sec@1024 bytes/frame,

[0961] 102000 frames/sec@512 bytes/frame,

[0962] 204000 frames/sec@256 bytes/frame.

[0963] The following calculations assume 250 instructions/frame, 45 nsecclock. Thus S=250*45 nsecs=11.2 usecs. Thruput Utilization Response Nbrin system Av Frame Size (X) (U) (R) (N) 1024 51200 0.57 26 usecs 1.3 512102000 >1 — — 256 204000 >1 — —

[0964] Lets look at it for varying instructions per frame assuming 512bytes per frame average. Nbr in Instns Per Service Thruput UtilizationResponse system Frame Time (S) (X) (U) (R) (N) 250 11.2 usec 102000 >1 —— 250 11.2  85000 (*) 0.95 224 usecs 19 250 11.2  80000 (**) 0.89 101  8225 10 102000 1.0 — — 225 10  95000 (*) 0.95 200 19 225 10  89000 (**)0.89  90  8 200  9 102000 0.9  90  9 150  6.7 102000 0.68  20  2

[0965] If 100 instructions/frame is used, S=100*45 nsecs=4.5 usecs, andwe can support 256 frames: 100 4.5 204000 0.91 50 10

[0966] Note that these calculations assume that response times increaseexponentially as utilization increases. This is the worst-caseassumption, and probably may not be true for our system. The figuresshow that to support a theoretical full 4*100 Mbit receive load with anaverage frame size of 512 bytes, there will need to be 19 active “jobs”in the system, assuming 250 instructions per frame. Due to SRAMlimitations, the current design specifies 8 SRAM buffers for activeTCBs, and not to swap a TCB out of SRAM once it is active. So underthese limitations, the INIC will not be able to keep up with the fullframe rate. Note that the initial implementation is trying to use only 8KB of SRAM, although 16 KB may be available, in which case 19 TCB SRAMbuffers could be used. This is a cost trade-off. The real point here isthe effect of instructions/frame on the throughput that can bemaintained. If the instructions/frame drops to 200, then the INIC iscapable of handling the full theoretical load (102000 frames/second)with only 9 active TCBs. If it drops to 100 instructions per frame, thenthe INIC can handle full bandwidth at 256 byte frames (204000frames/second) with 10 active CCBs. The bottom line is that allhardware-assist that reduces the instructions/frame is reallyworthwhile. If header-assist hardware can save us 50 instructions perframe then it goes straight to the throughput bottom line.

1. A method for network communication, the method comprising: receivinga plurality of packets from the network, each of the packets including amedia access control layer header, a network layer header and atransport layer header; processing the packets by a first mechanism, sothat for each packet the network layer header and the transport layerheader are validated without an interrupt dividing the processing of thenetwork layer header and the transport layer header; sorting thepackets, dependent upon the processing, into first and second types ofpackets, so that the packets of the first type each contain data;sending the data from each packet of the first type to a destinationwithout sending any of the media access control layer headers, networklayer headers or transport layer headers to the destination.
 2. Themethod of claim 1, wherein processing the packets by a first mechanismfurther comprises: processing the media access control layer header foreach packet without an interrupt dividing the processing of the mediaaccess control layer header and the network layer header.
 3. The methodof claim 1, further comprising: processing an upper layer header of atleast one of the packets by a second mechanism, thereby determining thedestination, wherein the upper layer header corresponds to a protocollayer above the transport layer.
 4. The method of claim 1, furthercomprising: processing an upper layer header of at least one of thepackets of the second type by a second mechanism, thereby determiningthe destination.
 5. The method of claim 1, further comprising:processing a transport layer header of another packet by a secondmechanism, prior to receiving the plurality of packets from the network,thereby establishing a Transport Control Protocol (TCP) connection forthe packets of the first type.
 6. The method of claim 1, wherein sortingthe packets includes classifying each of the packets of the first typeas having an Internet Protocol (IP) header and a Transport ControlProtocol (TCP).
 7. The method of claim 1, further comprising:transmitting a second plurality of packets to the network, each of thesecond plurality of packets containing a media access control layerheader, a network layer header and a transport layer header, includingprocessing the second plurality of packets by the first mechanism, sothat for each packet the media access control layer header, the networklayer header and the transport layer header are processed without aninterrupt dividing the processing of the media access control layerheader, the network layer header and the transport layer header.
 8. Themethod of claim 1, wherein the first mechanism is a sequencer runningmicrocode.
 9. A method for communicating information over a network, themethod comprising: obtaining data from a source allocated by a firstprocessor; dividing the data into multiple segments; prepending a packetheader to each of the segments by a second processor, thereby forming apacket corresponding to each segment, each packet header containing amedia access control layer header, a network layer header and atransport layer header, wherein the prepending of each packet headeroccurs without an interrupt dividing the prepending of the network layerheader and the transport layer header; and transmitting the packets tothe network.
 10. The method of claim 9, wherein prepending a packetheader to each of the segments by a second processor further comprises:prepending the media access control layer header for each packet withoutan interrupt dividing the prepending of the media access control layerheader and the network layer header.
 11. The method of claim 9, whereineach packet header contains an Internet Protocol (IP) header and aTransport Control Protocol (TCP) header. the media access control layerheader,
 12. The method of claim 9, further comprising establishing aTransport Control Protocol (TCP) connection by the first processor andusing the connection to prepend the packet header to each of thesegments by the second processor.
 13. The method of claim 9, furthercomprising creating a template header and forming each packet headerbased upon the template header.
 14. The method of claim 9, whereinobtaining data from the source in memory allocated by the firstprocessor is performed by a Direct Memory Access (DMA) unit controlledby the second processor.
 15. The method of claim 9, further comprisingprepending an upper layer header to the data, prior to dividing the datainto multiple segments.
 16. The method of claim 9, further comprising:receiving another packet from the network, the other packet containing areceive header including information corresponding to a network layerand a transport layer; and selecting whether to process the other packetby the first processor or by the second processor.
 17. A method forcommunicating information over a network, the method comprising:providing multiple segments of data; prepending an outbound packetheader to each of the segments, thereby forming an outbound packetcorresponding to each segment, the outbound packet header containing anoutbound media access control layer header, an outbound network layerheader and an outbound transport layer header, wherein the prepending ofeach outbound packet header occurs without an interrupt dividing theprepending of the outbound media access control layer header, theoutbound network layer header and the outbound transport layer header;transmitting the outbound packets to the network; receiving multipleinbound packets from the network, each of the inbound packets includingan inbound media access control layer header, an inbound network layerheader and an inbound transport layer header; processing the inboundpackets, so that for each packet the inbound network layer header andthe inbound transport layer header are validated without an interruptdividing the processing of the inbound network layer header and theinbound transport layer header.
 18. The method of claim 17, wherein theprocessing the inbound packets is performed simultaneously with theprepending the outbound packet header to each of the segments.
 19. Themethod of claim 17, further comprising creating a template header andusing the template header to form each outbound packet header.
 20. Themethod of claim 17, wherein providing multiple segments of data includesdividing a block of data into the segments.
 21. The method of claim 20,further comprising prepending an upper layer header to the block ofdata, prior to dividing the block of data into multiple segments. 22.The method of claim 17, further comprising: sending data from eachinbound packet to a destination without sending any of the media accesscontrol layer headers, network layer headers or transport layer headersto the destination.
 23. The method of claim 17, further comprising:processing an upper layer header of at least one of the packets by asecond mechanism, thereby determining the destination, wherein the upperlayer header corresponds to a protocol layer above the transport layer.24. The method of claim 17, further comprising: processing a transportlayer header of another inbound packet, prior to receiving the pluralityof packets from the network, thereby establishing a Transport ControlProtocol (TCP) connection for the inbound packets.